# McCulloch Carburetors



## heimannm (Jan 16, 2010)

NOTE: Since the hack the photos were lost, I am trying to put this back together with some additional information I have picked up along the way.

Legal Disclaimer - what I am about to post is based on my experiences and research. I am a relative newb on the whole matter as I have only been messing with these for a couple of years. This comes with no promises except that I have done my best to describe things as well as I can. I welcome anyone to add their comments, suggestions, recommendations, etc.

Many are reluctant to work on the old McCulloch carburetors because they are not Tillotson HL's or other more familiar models. In addition, most of the old Mac's have a primer in place of a choke, which adds to their mystery and in many cases their tendency to be leaky. On top of that, the diaphragms that we can get today are pretty expensive, normally $30 for the set of metering and fuel pump diaphragms with their gaskets.

I have several saws with the old McCulloch carburetors and have been struggling with a few of them myself so lately I decided to just try and document step by step what I've been doing in hopes of helping others, as well as prompting some of you to jump in with better ideas and solutions where applicable.

I will be showing several different saws and carburetors as we go through this, but will try to make it flow in a reasonable logical manner to make it as easy to follow as possible.

Let's get started:

Here is my 795, this carburetor looks pretty bad, but the saw did run, just not very well.







On this saw I had to make a clip to hold the throttle push rod. I don't think the push rod was stock, or maybe the carburetor had been switched already. There should have been a little clip on the carburetor for the rod to slide through but the rod is so bent up it would never have worked anyway.




This is what the clip is supposed to look like. See the spring on the throttle shaft? More on that in the next post.




On this saw, there is no solid connection between the throttle push rod and the levers on the throttle shaft. When the push rod come forward it pushes the lever forward, and when the throttle is released it shuttles and pulls the other lever back.




Mark


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## heimannm (Jan 16, 2010)

Many of these older McCulloch carburetors have an "idle speed governer", the throttle plate is off center so the velocity/pressure of the air moving through pulls the throttle shut. There is a tiny spring on the throttle shaft that pulls the throttle open. If you notice there are notches in the lever that allow you to adjust the spring to control how hard it pulls open, off setting the velocity/pressure through the carburetor.

At very low speeds, as the velocity/pressure drops the spring pulls the throttle open. It is a little unnerving at times to have an idling saw start to "hunt" speeding up and slowing down. Usually is speeds enough to move the chain a bit. I guess this was not a problem in the good old days when sawyers were men and lawyers were scarce.




Another Mac carburetor with the idle speed governor.




If you take the throttle shaft out, make sure the spring is to the left of the screw that hold the shaft clip in place.

The idle speed screw does ultimately control the minimum idle speed, the idle speed governer simply helps keep the engine running, sort of a built in throttle blipping device.

Mark


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## heimannm (Jan 16, 2010)

While we are on the subject of governers, I also have a 740 with an air vane governer. On this saw the spring loaded air vane governer pulls the throttle open and a high speeds the air flow from the flywheel pushed the air vane closing the throttle. This is how it was done before the days of RPM limited electronic coils. Again the throttle linkage is not directly connected to the lever, but simply allows the spring loaded air vane to push the throttle open (or closed, depending on engine speed).

All together




This is a stock clip with the throttle push rod sliding through a small groove in the casting under the clip. Other saws even have a small felt wick in the casting that can be oiled to keep the shaft lubricated. Hey, that's a good idea, I will have to add that to this saw.




Here is a view of the arm of the air vane governer slipped over a lever arm on the opposite side of the throttle shaft.




Throttle closed, the spring on the throttle trigger pulling the rod back and overcoming the spring on the air vane trying to pull the throttle open.




Throttle rod extended forward, I don't know if you can see it but the rod has moved completely away from the lever on the throttle shaft and the spring on the air vane is pushing the throttle open.




Mark


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## grandpatractor (Jan 16, 2010)

This is very interesting ,Mark!


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## heimannm (Jan 16, 2010)

When removing these carburetors, I like to use a screwdriver and push the primer all the way forward and slip the linkage/push rod out.




To make a little more room to loosen the bolts, I was able to slip the fuel line off at the tank on this saw.




Other saws like my 795 have a molded fuel line coming through in the same spot and you just have to work around those. On the 795 I saw that there was a bit of leakage where the line went through the fuel tank. I read in another thread one way to solve this was to wrap a little teflon tape around the line, so I tried it and voila, no more leak.







Mark


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## crmyers (Jan 16, 2010)

Good stuff, keep it coming.


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## heimannm (Jan 16, 2010)

Now the carburetor is out, as I mentioned this one is pretty rough. This one has the fitting for the "fuel collector" hose that connects to the spit back shield at the back of the air box.




The idea is that since these reed valve engines will leak a little pressure back through the carburetor, the spit back shield collects the expelled fuel and the hose pulls it back into the carburetor. That's the theory anyway. The fuel collector line is disconnected from the carburetor in this view, that's another part of the story.




On the other side, is the infamous McCulloch primer.




Primer off, there are two o-rings that seal the primer to the carburetor body. Either standard #010 or #011 o-rings will work.




I use a small dental pick to work the "o-ring" out, this is in fact a square cross section rubber plug that the .125" diameter steel ball seals against. The spring keeps the ball seated until the primer is depressed, then the fuel discharged from the primer squirts directly into the space on top of the reed valves.

Here are the parts in order:




Mark


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## heimannm (Jan 16, 2010)

The gasket that seals the carburetor to the air box is the same one used on the Tillotson HL carburetors. Notice that there are multiple holes for the impulse signal that runs the fuel pump. For whatever reason, the McCulloch (Walbro) and Tillotson carburetors have the impulse ports in a different location. Keeping this in mind can save a lot of headaches when you are switching carburetors.




Flip it over and remove the four screws holding the carburetor together. You may notice this is not the same carburetor as shown in the other photo's. I compiled this from several different carburetors I have been working on. Don't let this distract you too much.




The meter lever and needle are very similar to the Tillotson HS and Walbro SD type carburetors, the shaft is held in by a small 4-40 screw.




Here are the parts disassembled in order, the seat has a 5/16" hex just like the Tillotson HL series, needle, lever and pivot, spring, and the screw.




Mark


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## heimannm (Jan 17, 2010)

The metering diaphragm & gasket. The new one is on the left, and an example of the old one on the right. It just occurred to me looking at the photo's that the new one has a "button" in the center, the old one was flat. Later on we'll see the metering lever is to be set flush with the body of the carburetor, how is that supposed to work if the plate on the diaphragm is flat?




The new gasket and diaphragm in the relative position they will be installed. So far so good but look, the new diaphragm has some additional holes around the perimeter.




And guess what, on some of the carburetor bodies the hole overlaps the O.D. of the bowl over the diaphragm. It took me about 6 tries on one carburetor to figure out where the awful leak was coming from. On another body, the dimensions were different and the hole was sealed. Look carefully and you can see the hole is partially uncovered in this case.




My solution? A little Seal & Stick solvent resistant adhesive/sealer. Just a little dab to fill the holes and stick the gasket and diaphragm together to prevent leaking past the hole.




What I am learning since first posting this thread some while back is the metering diaphragms with the "extra" holes are really for the kart carburetors, BDC models, etc.

Mark


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## eyolf (Jan 17, 2010)

Many years ago I was parts and service guy for a small midwestern lawnmower disributor. Near the end of my employment, the Jacobsen company came out with a new ridng mower called the RMX, and it had a few serious problems in the drive system.

I stumbled onto a solution or two, and wanted to put together a pamphlet with nice photos and instructions. Cost was breathtaking. You've put together a presentation that puts what I had in mind, then, to shame. And the cost was, well, lets say "affordable"

Aint technology great?

And great job, BTW!


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## heimannm (Jan 17, 2010)

I suppose at some point I should mention that the whole thing needs to be cleaned up while everything is taken apart. I usually remove the H and L needles as well as the metering needle and try to clean all of the bores and passages with aerosol carburetor cleaner. So far I haven't run into many that needed more than that in the way of cleaning the gunk out.

Before installing the new metering needle, I thought I'd measure up a relatively new one for the sake of comparison. Here is the lever and pivot, spring, and needle. The new spring is 1/2".




And here is the metering needle installed in the body of the carburetor. Now I see how the flat plate on the original diaphragm works, sorry but I got confused for a minute as I did an SDC carburetor today as well. Look at one of those (SDC carburetor) and you will see the the lever is in a sort of notch in the body of the carburetor and only the "button" on the plate attached to the metering diaphragm will activate the lever.




The meter lever is to be set flush with the body of the carburetor. I have had a few problems with flooding if the lever gets a bit too high. I try to keep it flush or .005 to .010" low.




Mark


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## heimannm (Jan 17, 2010)

Thanks eyolf, I am hoping that others with more and better information will jump in and supplement what I am trying to do here.

Now for the fuel pump. If you get the parts from Bob, chances are the fuel pump will be three separate loose pieces, two gaskets and the valve/diaphragm piece.

The Bob kit, metering diaphragm and gasket on the left, fuel pump diaphragm/valve in the center, fuel pump gaskets on the right.




The OEM part was a sort of sandwich, with the diaphragm/valves between the gaskets, special little slots for the valves to fit through, and stapled together. OEM kit on the right



When I first started struggling with these carburetors, I tried all sort of combinations, making a sandwich like the original, using only one gasket with the diaphragm flat against the fuel pump body, two gaskets on one side with the diaphragm flat against the fuel pump body, O.K. you get the idea.

What did I learn? If you prime the carburetor manually, any combination will work. I have only had success with the McCulloch primer working if the diaphragm is flat against the fuel pump body with the OEM type diaphragm and gasket set up. I am not sure if that is real, or if it just worked out that the "sandwich" attempts had other problems with the primer circuit. Anyone else out there have any ideas/experience?

The Bob diaphragm/valve laying flat on the fuel pump body.




The Bob diaphragm and gasket, diaphragm below and gasket on top.




I thought perhaps the three piece Bob Johnson parts were actually for the kart carburetors, like some of the metering diaphragms you might get from Bob, but looking at the carburetor book I see that all of the MAC and BDC carburetors use the same fuel pump diaphragm/gasket combination, PN 57274. Anyone else out there have something to add?

Mark


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## heimannm (Jan 17, 2010)

I thought as long as I had it apart, I would measure the primer spring as well. Looks to be just over 3/8" long. I measured the steel ball and confirm that the IPL's that describe it as 1/8" are correct, some incorrectly call out 1/4" diameter. Also confirming the o-rings that seal the primer to the carburetor can be either #010's or #011's.







Also confirming an earlier mention, the gaskets that seal the carburetor to the air box are same shape as the Tillotson HL, makes sense since the carburetors will also interchange, but the impulse ports are in a different location. I have not made mention that the impulse to run the fuel pump in the carburetor comes through the flange on the front of the carburetor. In every case make sure the gasket has a hole that aligns with the carburetor and airbox.







One more thing while I remember, the OEM o-ring on the needles is also a square profile, but I have found an standard #004 o-ring will also work pretty well.




Mark


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## hexen71 (Jan 17, 2010)

I have nothing to add but keep up the good work because I find it very informative and will be using this gide in the next few weeks as I just acquired 5-10e


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## crmyers (Jan 17, 2010)

This should be a sticky.


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## heimannm (Jan 17, 2010)

Do the carburetors work after I got done messing with them?

As I mentioned, I can't make the McCulloch primers work with the Bob fuel pump gaskets/diaphragm/valves, but on the 640 with the OEM type it works fine. Since I don't use these saws for regular cutting, I don't mind priming them manually to get them to start, and once started they will restart if they don't set for too long.

I am not sophisticated enough for video, and I don't have any logs to cut anyway so you will have to trust me on the photo's of the tach being representative. You could also ask my son Jeff since he came to help this afternoon and saw all three (640, 740, 795) running.

The 640 WOT unloaded - this one really surprised me. If I remember correctly (it has been a long time since I first started on this thread) I did have to go back through that carburetor and reset the metering lever height to keep it from leaking fuel when it was setting.




The 740 idle and WOT







The 795 idle and WOT, it started to run out of fuel just as I was trying to snap the photo but I swear I saw it go over 9,000.








Well guys, that's it for tonight. I hope some of you find this helpful, and other will pipe up and let us all know how we can do even better.

Oh, does anyone know where I can get about 6 of the metering needles for the McCulloch carburetors as well as a few extra primer seats? After all this I still have a few leakers and it appears to be coming out of the carburertor throat while the saw is setting not running.

Thanks!

Mark

NOTE: I am 99% sure now that the metering needles from the SDC carburetor will work in the MAC carburetors. I did manage to find some of the seats as well, now if I just had time to stay home and work on saws...


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## Justsaws (Jan 17, 2010)

Very good tutorial.

It looks like you would have to mount the AM fuel pump the way that you did to get it to push prime. Is it necessary to use both gaskets on the AM kit to get the needed clearance for the pump and flaps valves to function?

I missed the part about not being able to get the primer to work with the AM kit. Any chance that using the gasket with the slots from the OEM kit with his pump would fix that?


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## heimannm (Jan 17, 2010)

hexen71 said:


> I have nothing to add but keep up the good work because I find it very informative and will be using this gide in the next few weeks as I just acquired 5-10e



Is your 5-10E an electric start? Cool beans, I have a 3-10E and a 5-10. The 3-10 has a Walbro SDC carburetor, the 5-10 had the McCulloch flat back/bullfrog but someone beofre me converted it to a Tillotson HS I believe.

The 10 Series flat back/bullfrog is another animal altogether. I have a little experience with them so far, more to go there certainly. Perhaps as some point in the future I will gain some additional practice with the 10 Series and try to do something with those as well.

Good news is the primers are very good if you have all the right parts. Bad new is the little duck bill check valves are virtually impossible to find anymore.

Mark


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## heimannm (Jan 17, 2010)

Justsaws said:


> Very good tutorial.
> 
> It looks like you would have to mount the AM fuel pump the way that you did to get it to push prime. Is it necessary to use both gaskets on the AM kit to get the needed clearance for the pump and flaps valves to function?
> 
> I missed the part about not being able to get the primer to work with the AM kit. Any chance that using the gasket with the slots from the OEM kit with his pump would fix that?



I have not been able to locate the OEM fuel pump kit, only the parts I have received from Bob. B200 told me he got some from Bob and they were the OEM style. Bob has lots of stuff and his inventory changes a lot so you get what he has when you order.

Mark


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## Justsaws (Jan 17, 2010)

heimannm said:


> I have not been able to locate the OEM fuel pump kit, only the parts I have received from Bob. B200 told me he got some from Bob and they were the OEM style. Bob has lots of stuff and his inventory changes a lot so you get what he has when you order.
> 
> Mark



It is late and I might not being seeing the obvious answer in the photos. What I was asking about is whether or not you could use the old OEM gasket with the slots in it and the new AM pump diaphragm from Bob's kit in order to get the full up down motion restored to the fuel pump.


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## hexen71 (Jan 17, 2010)

yep mine is the electric start


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## belgian (Jan 17, 2010)

Justsaws said:


> It is late and I might not being seeing the obvious answer in the photos. What I was asking about is whether or not you could use the old OEM gasket with the slots in it and the new AM pump diaphragm from Bob's kit in order to get the full up down motion restored to the fuel pump.



First want to say that Mark did a real nice job detailing this carb work. Very helpfull and I'm looking forward to the "Bullfrog carb review" in the future. 

I would assume that when the carb pump is working fine during operation, I see no particular reason that the gasket assembly would not be working properly during the primer operation. Hence, If the primer is not working, I'd check probably if the primer assy is working OK, especially the vacuum function (O-rings) and the fuel passages. Is there a possibility that the AM set is blocking a fuel passage ? Just a wild guess, of course but something maybe worth checking.


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## lawnmowertech37 (Jan 17, 2010)

heimannm said:


> I have not been able to locate the OEM fuel pump kit, only the parts I have received from Bob. B200 told me he got some from Bob and they were the OEM style. Bob has lots of stuff and his inventory changes a lot so you get what he has when you order.
> 
> Mark



mark what is the part # for the fuel pump kit ?


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## GASoline71 (Jan 17, 2010)

Mark... fantastic thread mang!   

I have a Flatback that came out of my 640 that is just sittin' on the work bench. It is is great shape, but needs a rebuild...

Thanks for the detailed pics and info!

Gary


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## Justsaws (Jan 17, 2010)

belgian said:


> First want to say that Mark did a real nice job detailing this carb work. Very helpfull and I'm looking forward to the "Bullfrog carb review" in the future.
> 
> I would assume that when the carb pump is working fine during operation, I see no particular reason that the gasket assembly would not be working properly during the primer operation. Hence, If the primer is not working, I'd check probably if the primer assy is working OK, especially the vacuum function (O-rings) and the fuel passages. Is there a possibility that the AM set is blocking a fuel passage ? Just a wild guess, of course but something maybe worth checking.



I do not know for sure but the space created by the cut gasket between the body and the pump diaphragm might allow the primer to pull and push the fuel through the carb. By removing the cut gasket and placing the diaphragm flush against the body the primer may not be able to move the diaphragm through the full range of motion and render the primer in effective.


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## sawbones (Jan 17, 2010)

Great job Mark 

One of these days I will need to tinker with some flatbacks I have on a few runners.

Now you need to link this thread into your signature..

Here is an ad I found yesterday,

It is from 1975.


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## heimannm (Jan 17, 2010)

Calvin, the OEM metering diaphragm/gasket is 55067 and the fuel pump diaphragm/gasket is 57274. The seat for the primer is 59480.

The little duck bill for the 10 Series carburetor is 63041.

Sawbones, thanks, I still enjoy teaching I guess. It never occurred to me that the McCulloch carburetors were made for them by Walbro, even though I have seen the McCulloch branded SDC carburetors. Very neat information. I added a link to this thread to my signature, but I had to get rid of some saws to do it.

Justsaws, now I understand your point. Problem is most of the time the old gaskets are shot and can't be reused. If I were a lot more patient and had fine motor skills I suppose it would be possible to cut new ones but for now I don't think it's possible for me.

Roland, I will have to look things over again this week and see if I can learn anything further about how it's supposed to work and what is going wrong.

Always something more to think about and try in any case.

Mark


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## lawnmowertech37 (Jan 17, 2010)

heimannm said:


> Calvin, the OEM metering diaphragm/gasket is 55067 and the fuel pump diaphragm/gasket is 57274. The seat for the primer is 59480.
> 
> The little duck bill for the 10 Series carburetor is 63041.
> 
> ...



thanks mark


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## brokenbudget (Jan 17, 2010)

heimannm said:


> Is your 5-10E an electric start? Cool beans, I have a 3-10E and a 5-10. The 3-10 has a Walbro SDC carburetor, the 5-10 had the McCulloch flat back/bullfrog but someone beofre me converted it to a Tillotson HS I believe. Mark



mark, it's my understanding that they came with both. the flat backs were on the earlier models (within the first year or 2). 
when i first came here i was going to fix up a 10-10E (sure did look like it said 1-10E). it had the flat style carb on it, but both my "newer" 10-10E 
and 5-10E have the walbro on them.
it was also my understanding they kept the flatty around for the bigger saws as they flowed much better.

oh yeah, my 5-10E's electric start works very well. just finished another battery pack for the 10-10E but there is still something wrong either with the switch or in around the windings. i have to 'help' the saw to start turing over. once you get the first spin it will turn the saw over (decomp working fine) it seem that the motor is a little low on power. could be one of the rectifiers in the switch or a weak winding.


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## cpr (Jan 17, 2010)

heimannm said:


> Oh, does anyone know where I can get about 6 of the metering needles for the McCulloch carburetors as well as a few extra primer seats? After all this I still have a few leakers and it appears to be coming out of the carburertor throat while the saw is setting not running.
> 
> Thanks!
> 
> Mark



Just a thought, but I had the same problem with my Tilly HL on my 795. I checked everything and the answer was the brass nozzle for the metering valve was over torqued. I reset it minus torque wrench, but it was just barely seated, no pressure on it whatsoever. Leak gone. BTW, no I have not had time to figure out what the "noise" was on it. Maybe this week.

Great thread and very inspiring!!!


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## lawnmowertech37 (Jan 17, 2010)

mark i found something that may interest folks is a mcculloch carburetors manuel and repair book with parts lists diagrams of all the mac carbs in it it was in a mcculloch book i got from someone 

also has repair manuels for basically all the mac models 

not to mention parts lists 

that book is about 7 inchs diameter


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## heimannm (Jan 22, 2010)

I had a chance this week to meet Joe Salva from Sugar Creek Supply. This company produces carburetor kits as well as decals, etc. for a lot of saws that are NLA anywhere else.

Prices are quite reasonable as well.

I picked up a few kits for the McCulloch/Walbro flat back carburetors off the big saws, as well as one for the Carter ND on my Wright GS5020A.

You can find more details over at cscc.se

Mark


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## lawnmowertech37 (Jan 23, 2010)

heimannm said:


> I had a chance this week to meet Joe Salva from Sugar Creek Supply. This company produces carburetor kits as well as decals, etc. for a lot of saws that are NLA anywhere else.
> 
> Prices are quite reasonable as well.
> 
> ...



Yea Joe is gifted in that area


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## heimannm (Feb 15, 2010)

I put one of Joe's (Sugar Creek Supply) kits in a McCulloch 440 a few weeks ago, saw did not seem to run right but I thought maybe it was seals, etc. 

I found out this weekend that the plug wire was broken, spark was intemittent, replace the coil and the saw now runs very well.

Thanks to Joe, reasonably priced kits for the McCulloch/Walbro Mac carburetors are readily available.

Mark


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## hep1023 (Mar 10, 2010)

crmyers said:


> This should be a sticky.



where can i find a metering diafragm and oil pump diafragm for mac '(à ?


number on carb is 61853A


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## kev1n (Mar 10, 2010)

*small mcculloch flatback*

hey guys, i'm having some troubles with a 1-76. i rebuilt the carb and the saw runs great but when i shut it off it just keeps spitting gas out the carb until all the gas in the carb and fuel line is drained. also the pump isn't working that good. any clues as to what to look at first when i tear this apart again. thanks kev1n


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## heimannm (Mar 10, 2010)

hep - if your carburetor looks like the McCulloch carburetors in this thread, you can get the kits from Joe Salva at Sugar Creek Supply, you can also find a link to Joe over as Chainsaw Collectors.se

kev1n - 1st thing I'd do is check the height of the metering lever, should be flush with the body of the carburetor as shown in this thread, or the needle itself might be bad, as I mentioned they are available from Bob Johnson, or from just about any older Walbro carburetor.

You should also make sure the fuel line is tight, and that is isn't leaking where the hose passes through the fuel tank. I don't remember if the connection on the 1-76 is a fitting through the tank or a hose with a molded grommet, I had good luck wrapping teflon tape around the grommet on one saw as described in this thread.

It could also be the primer, they are rather notorious for leaking and are relatively expensive to replace (I think I paid $25 for the last one I got from Bob). On the other hand, with the primer in good condition starting the saw is a real pleasure.

Mark


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## kev1n (Mar 10, 2010)

thanks for the reply, it has the fitting between the tank. the gas is coming out of the hole in the center of the carb near the front. just keeps pouring out. does the sugar creek supply kit come with a new needle and seat?


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## heimannm (Mar 10, 2010)

None of the suppliers I have found include the needle with the diaphragms and gaskets. 

You can get a needle and lever from Bob, probably others as well as it is the same needle as used in the SDC carburetors on the 10 Series McCulloch saws. The levers are different between the SDC and the MAC carburetors, so the needle kit comes with both.

Mark


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## kev1n (Mar 10, 2010)

i've read your thread a few times. there is some great info there. thanks for putting it all together. i will try the method you did without the fuel pump gasket if everything else looks good.


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## heimannm (Mar 10, 2010)

Look carefully at the discusson regarding the metering diaphragm and the extra holes. If you have the parts that are meant for the kart carburetors there will be some holes uncovered that will let gas run out the atmospheric vent on the "dry" side of the metering diaphragm.

Mark


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## kev1n (Mar 10, 2010)

i did look carefully at that. i got mine from bob. it didn't have those holes yours did. i also picked up an oem 55067c off ebay. i was hopeing to save it but i might have to throw it in, it's not raised up with that nipple


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## cbfarmall (Mar 23, 2010)

Mark,

Thank goodness for this thread. I just picked up a nice 550 from a member here and you supplied an IPL and this great tutorial. Followed it to the letter, including your little tip about the extra holes in the metering diaphragm. Only had to remove the carb 1 time and that was to lower the lever height a touch as it was running very rich and flooding. I don't think the primer is working, but what else is new? Now, I may go pull out my 890 with SP125 power and fix that carb, again.

Chris B.


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## stinkbait (Mar 25, 2010)

*I would like to add to the thread*

If the rubber seat for the primer pump check valve happens to bad you can replace it with the rubber seat from a Tillotson HL inlet needle seat. Check it out.


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## leeha (Mar 25, 2010)

Nice Stinky.
Great tip.
I will remember that.

Thanks

Lee


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## stinkbait (Mar 26, 2010)

Yeah, I figured that out last night while rebuilding the mac flatback off of my 440. Now, with the new rubber seat, the primer works like a charm.


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## blsnelling (May 18, 2010)

Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.


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## stinkbait (May 18, 2010)

blsnelling said:


> Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.



The kits that I bought didn't come with any. You may have to get them made.


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## blsnelling (May 18, 2010)

It seems like I've seen a source for different size welch plugs. I can't seem to find it though. I think it was FATGUY that showed me, and he's not available right now.


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## Urbicide (May 18, 2010)

blsnelling said:


> Does anyone know if welch plugs are available for these carbs? I just cleaned up a super corroded one and had to pull them.




Mac part # 110179 Plug, expansion 1/2"

Mac part # 104407 Plug, expansion 1"


Don't know if the numbers are current or not. Mac loved changing part numbers. Probably could find some generic plugs at a good *** dealer or auto parts store. I would use some sealer around the edges of the replacements since the corrosion & cleaning operation might have slightly enlarged the actual openings a bit in the carb body.




(Nice job, Brad, on cleaning that carburetor. Looks good. You should get into the used car refinishing business. )


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## Urbicide (May 18, 2010)

blsnelling said:


> It seems like I've seen a source for different size welch plugs. I can't seem to find it though. I think it was FATGUY that showed me, and he's not available right now.



He must be in the can. :greenchainsaw:


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## blsnelling (May 18, 2010)

Urbicide said:


> He must be in the can. :greenchainsaw:



I think he's home sick in bed


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## blsnelling (May 18, 2010)

Here it is, thanks to Nik. Expansion Plugs


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## Urbicide (May 18, 2010)

blsnelling said:


> I think he's home sick in bed



Nik, hope you get to feeling better soon!


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## heimannm (Jul 25, 2010)

More to add...

I was making sure my 550 would be ready in case I get to go the the GTG in Illinois next Saturday. The saw would start and idle just fine but when I ran it up to full speed it would simply run out of fuel. No adjusting of the High Speed jet would help.

I started out by replacing the diaphragms assuming one or the other was a bit stiff but no improvement there.

I then replaced the fuel filter (felt plug in the bell at the end of the fuel line) but no improvement there either.

I then replaced the pick up line altogether but still no improvement.

O.K., time to get more serious. I took the carburetor completely apart and popped out the large expansion plug and tried a shot of carburetor cleaner in the hole and could actually hear the check valve pop free. To make sure, I popped out the smaller expansion plug and shot come carburetor cleaner through those hole as well.

Put it back together and once again it runs like a top. Not sure why the check valve got stuck, but I had run the saw enough that it should have come loose if it ever was going to on its own.

The check valve is closed under low speed conditions, but opens up at high speed to provide the extra fuel needed. I could not figure out out to remove the seat so I simply shot the carburetor cleaner through several times and gave it a blast of air as well to make sure everything was clear.

Now I need to check out the source for expansion (welch) plugs as I need a small supply of 1/2" and 1" plugs to allow me to work on several remaining McCulloch carburetors.

I didn't take time to photograph this one with the expansion plug out, but I will do that next time assuming I can find some more plugs.

Mark


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## Brian13 (Jul 25, 2010)

Bob Johnson had the ones for me. I replaced both plugs.


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## heimannm (Jul 25, 2010)

I guess I will be calling Bob on Monday, I am sure I can think of a few more things to pick up at the same time.

There I was thinking I got all the plugs he had some while ago...

Mark


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## Brian13 (Jul 25, 2010)

I believe he even had the check valves, he was at least asking me if mine were still good.


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## cpr (Nov 22, 2010)

Fighting with one of these for a Super 250. No primer, it's the model specific choke carb.

I'm a little stumped. I have a Sugar Creek kit for it, but I can't get it to pass fuel. I am tempted to play around with gasket stacking like Mark did, but of the 6 times I've tried, only once have I managed to get fuel to the pump chamber and beyond and I am unable to identify why it worked that one time. At no time, however, have I been able to make the saw run on anything other than a shot down the bore. Runs like a champ for 4 seconds when I do that! Just enough to tease me. In addition to the gasket stack, I have concern with the fuel filter pressed into the bottom. For now, that part is resting in a carb cleaner dip tank overnight to see what happens. I'll eliminate that problem source if all goes well tomorrow. I can make air go through evey passage on the carb, no blockages I can identify. I have not pulled the welch plugs only because I don't have any... yet?

Getting good with this thing. I can go from spread on the bench to installed test and back out to spread on the bench in under 5 minutes...

A few pictures. One thing different (besides the choke in place of the primer) is the metering seat is pressed in, not threaded.






Sugar Creek Kit like the OEM.






Casting on the front. I assume it was made in October 1973.


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## stinkbait (Nov 22, 2010)

cpr said:


> Fighting with one of these for a Super 250. No primer, it's the model specific choke carb.
> 
> I'm a little stumped. I have a Sugar Creek kit for it, but I can't get it to pass fuel. I am tempted to play around with gasket stacking like Mark did, but of the 6 times I've tried, only once have I managed to get fuel to the pump chamber and beyond and I am unable to identify why it worked that one time. At no time, however, have I been able to make the saw run on anything other than a shot down the bore. Runs like a champ for 4 seconds when I do that! Just enough to tease me. In addition to the gasket stack, I have concern with the fuel filter pressed into the bottom. For now, that part is resting in a carb cleaner dip tank overnight to see what happens. I'll eliminate that problem source if all goes well tomorrow. I can make air go through evey passage on the carb, no blockages I can identify. I have not pulled the welch plugs only because I don't have any... yet?
> 
> ...



Been fighting witn the same crap on my mcculloch 440. i just gave up for a while I'm sure that I will get back to it one day. I bought the sugar creek kit and the kit from discount marine, and no luck.


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## cpr (Nov 23, 2010)

Anyone? Anyone? Bueller? Bueller?


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## heimannm (Nov 23, 2010)

Are you sure the pulse port is open in the carb, gaskets are not blocking the ports, the internal port in the air box is open to the crankcase?

I usually tap the carburetor down a bit before final tightening of the screws to make sure the holes in the gasket and ports are all aligned.

Mark


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## cpr (Nov 23, 2010)

Yep, open in the crank and through the carb. Pretty sure I had the carb "down" all the way.

One thing I did notice is the new gaskets between the carb and the tank body are thinner and the needle boot doesn't line up good anymore. Not a big deal, just an observation.

I found a new carb fuel filter. I may buy it and try switching them out.

Thanks Mark, at least I'm on the right track.


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## heimannm (Nov 23, 2010)

I've never had one that would not pull fuel after a prime, no matter how I had fuel pump diapragm and gaskets arranged, that's why I think it must be something else. 

Check all of the metering circuit as well, height of the metering lever, proper orientation of the gasket and diaphragm, make sure the passages are clear, you get the picture. If fuel can enter the metering section it won't run on it's own.
 
Even if the high speed passage is blocked, it should still idle though it would run out of fuel when the engine speeds up if fuel is pumping into the carburetor.

Mark


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## cpr (Jan 26, 2011)

After a several month's hiatus, I returned to the Super 250. Fixing that clutch drum last night left me no excuse to assemble it and try. I checked over the carb once, just to make sure, but changed nothing. Lo and behold it runs! Idles great and accelerates like mad, but the high jet isn't working. Guess I get to pull it once more, but I'm farther than I was.

First time the Super 250's done more than pop on a prime. I love my big bores, but goodness this thing is MEAN. Ferocious acceleration and the bark out of it is otherworldly, even for a Mac... No wonder you guys love them.


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## slipknot (Jan 26, 2011)

Wasnt this thread 2010 thread of the year? I know I learned so much from this thread alone it crazy...in fact once I understood things a little better I went from buying a mac 790 to get running and sell to get a mac 790 and then get mac 1-70 and many more macs...lol....i became a collector once I got my 790 running....once I cut wood I was hooked....watch out now...it could happen to anyone. Muscle saws are very addictive. Thanks Mark.


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## promac850 (Jan 26, 2011)

Subscribing... good info here.


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## cpr (Feb 16, 2011)

Finally, it's alive and behaving! Up to 3 saws to test and tune this weekend. Tomorrow, I'll attack a fourth languishing project before the 101s start arriving.


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## RandyMac (Feb 16, 2011)

So cpr, you are a convert to the mighty Supers. Too bad our muscle saws won't get to saw the wood they were intended to.
I'm switching out the choked Flatback on my Super, to a primer equipped one, with a larger venturi.


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## cpr (Feb 16, 2011)

May have to try that in there next. I have one in the rescued 790 that I won't be using in that saw.


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## Brian13 (Feb 16, 2011)

While we are on the subject of swapping out carbs for a bigger one, what about a BDC14 on a 797?


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## cpr (Feb 16, 2011)

Not sure there's sufficient room for the double pumper to fit. Plus the fuel intake would be straight down in the center. I've thought about it, but Lee says they don't fit.


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## leeha (Feb 16, 2011)

Brian13 said:


> While we are on the subject of swapping out carbs for a bigger one, what about a BDC14 on a 797?


 
Thats a no go. The BDC is much larger than the standard flatback or the 48890.
Plus the venturi is way to big for the intake system on the 797 or any saw.



Lee


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## Brian13 (Feb 16, 2011)

That is what I was wondering. I thought I saw one on a 797/101b once, but it was pretty heavily modified. It had a manifold between the block and tank. There is one on ebay right now for pretty cheap, so I figured I would investigate.


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## stinkbait (Mar 20, 2011)

I need some more info on the whole check valve assembly in these carbs. Apparently all the flatbacks don't have the check valve assembly. What's the deal with that? And, is there anything behind the small welch plug? I have a check valve kit with the new ball and seat and the new large welch plug. The instructions that came with the check valve kits shows the installation of the kit in a flatback carb that didn't initially have the check valve system. But the instructions doesn't give any info as to why it's needed or how it operates.


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## cpr (Mar 20, 2011)

stinkbait said:


> I need some more info on the whole check valve assembly in these carbs. Apparently all the flatbacks don't have the check valve assembly. What's the deal with that? And, is there anything behind the small welch plug? I have a check valve kit with the new ball and seat and the new large welch plug. The instructions that came with the check valve kits shows the installation of the kit in a flatback carb that didn't initially have the check valve system. But the instructions doesn't give any info as to why it's needed or how it operates.


 
I have one I need to install this week... I'll report my findings.


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## heimannm (Mar 23, 2011)

Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.

Mark


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## stinkbait (Mar 23, 2011)

heimannm said:


> Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.
> 
> Mark


 
Yeah, I took that out and installed the check valve assembly. I made the mistake of putting too much grease in the assembly to secure the ball. Had to remove the carb and flush it out with carb cleaner before I got the saw to run right. Now it runs like a brand new one.

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/LrgpzCKGH2s?hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/LrgpzCKGH2s?hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>


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## Eccentric (Mar 23, 2011)

heimannm said:


> Before they were equipped with the check valve, the flat back carburetors had another simple "capillary seal", like the sintered metal fuel filter but smaller.
> 
> Mark



The 1965 Supplement to the McCulloch 1-40/1-50/1-60 series service manual describes both valve systems in detail, and instructs technitians to replace the older capilary screen type setup with the ball type check valve when servicing older carbs.


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## wendell (Mar 24, 2011)

Took out the carb out on my Super Pro 70 and cleaned it up and still can't get the saw to fire (but it will sometimes act like it wants to). What are the base carb settings that i should start with? I'm used to 1 turn out on the H and L but not sure if that is correct for this saw. Also, is there any adjustment that needs to be made to the butterfly?


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## heimannm (Mar 25, 2011)

1 to 1-1/4 turns out from lightly seated for both H and L is a good place to start. 

If the saw has been setting for a long time it might help to give it a shot of prime right down the carburetor, then try pulling it with the throttle wide open. Sometimes you have to prime it and get the short burst two or three times before the carburetor starts pulling fuel on it's own.

That saw will have a pop up compression release, if it is leaking too much the saw may fire but not stay running. I have had some success fixing a leaking pop up with a dap of valve lap compound or even rubbing compound and polising up the valve and seat. Make sure you clean everything well before you put it back together.

Mark


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## wendell (Mar 25, 2011)

Thanks, I'll give that a try.


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## WKEND LUMBERJAK (Apr 17, 2011)

Subscribing


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## dieselsmoke (Apr 17, 2011)

Hellow Mark, I'm adjusting the mac carby on my newest saw, a Mac 790. This one has the Idle spring, tho it's not adjusted right. Shouldn't the tiny spring be pulling the throttle plate open, against the V shaped link on the end of the throttle shaft? when the saw is stopped and hands off the trigger? This is the first time I've tried to adjust this linkage. Thanks in advance. Brad.


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## Eccentric (Apr 17, 2011)

dieselsmoke said:


> Hellow Mark, I'm adjusting the mac carby on my newest saw, a Mac 790. This one has the Idle spring, tho it's not adjusted right. Shouldn't the tiny spring be pulling the throttle plate open, against the V shaped link on the end of the throttle shaft? when the saw is stopped and hands off the trigger? This is the first time I've tried to adjust this linkage. Thanks in advance. Brad.


 
You've got it Brad. The spring should pull the throttle plate open. When the engine's running at idle, vacuum will pull the throttle plate shut. The trick is finding the correct ballance. The throttle possiton will 'float' slightly. If you have the spring set with too much tension, the engine RPM will bounce excessively at idle. Too light, and it will tend to slow down and die.


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## dieselsmoke (Apr 21, 2011)

Eccentric said:


> You've got it Brad. The spring should pull the throttle plate open. When the engine's running at idle, vacuum will pull the throttle plate shut. The trick is finding the correct ballance. The throttle possiton will 'float' slightly. If you have the spring set with too much tension, the engine RPM will bounce excessively at idle. Too light, and it will tend to slow down and die.


 
Thanks Aaron, I missed this reply on the 17th. Played with spring settings the other nite, the saw is still not happy, so today I have re-read this entire post. I plan to make a final adjustment tonight and mount the carby for a test. This thread is really helpful, "a picture is worth a thousand words " thanks to everyone.


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## cpr (Apr 21, 2011)

Stick with it, it's rewarding. I must've had one in and out of saw 30 times and then spent the better part of an hour fiddling with the spring, the travel limiter and windmilling needles. Now that it's set though, it works great.


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## Brian13 (Apr 21, 2011)

cpr said:


> Stick with it, it's rewarding. I must've had one in and out of saw 30 times and then spent the better part of an hour fiddling with the spring, the travel limiter and windmilling needles. Now that it's set though, it works great.


 
Same here, and still dont think I have the spring tension just right.


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## cpr (Apr 21, 2011)

Yeah, mine probably surges and hunts just a little too much, but I like it doing that.


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## Brian13 (Apr 21, 2011)

I think I have the spring tension set a little too high. Dosnt want to come down all the way to idle, sticks on like a high idle, but once you get it to come all the way down its fine. So I am thinking the spring is pulling to hard for it to close like it should.


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## dieselsmoke (May 2, 2011)

Thanks guys for the help, I was cleaning the S-250 the other nite and found it Has a flatback with a choke butterfly. I had never looked that close befor, assumed it was a tilly HL. So, in I went. The PO had pinched the throttle arms tight to the rod, no "play" allowed. And they had rotated the gov spring the opposite direction so it closed the throttle butterfly. A quick tweek with the screw driver and adjust the spring the other way and presto, idle govener. this saw really responded well to the idle govener, It really works. 

I;m still searching for the right combo on the 790 tho. I'll get it yet.


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## heimannm (May 2, 2011)

It is satisfying to fix something, or make it "right" again, and have the machine respond as it is supposed to.

Congratulations on the Super 250, I am sure you will enjoy that one.

Mark


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## Sawchips (Sep 10, 2011)

Great thread!!!
All of your work is appreciated, "Thank you Mark" and the rest of you that contributed input.

Back in March a couple of you (CPR & Stinkbait) were getting ready to swap out the check ball assemblies in the carbs you were working on. How did that go? 
I'm going to have to do something with mine (Super 250) and I can't seem to find a new check ball, so I'm going to try and get mine out with out messing it up to bad. If I can do that I might be able to revers engineer the thing and make a new one. Of coarse I'm saying this with out have a clue as to what it looks like.
Did any of you happen to take any pictures of the check ball assembly or the bore in the carb body? Knowing what it looks like on the back side would help keep me from making a complete mess out of it. 

Thanks
Bob


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## Sawchips (Sep 11, 2011)

Bump.


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## heimannm (Sep 11, 2011)

The check ball and seat are sold as a kit (61155) or individual components ball (61151) and seat (61152). 

Try Bob Johnson (607 638 9297) for the parts, don't give up if you don't connect the first time or two that you call.

Note that you will need a 1" expansion plug for some of the carburetors (check valve is under the plug). It seems to me that some carburetors may have a threaded plug rather than the expansion plug but that could be a feeble old mind playing tricks on me.

Mark


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## Sawchips (Sep 12, 2011)

No Joy on the check ball assembly. 
Bob says someone from California bought out his remaining stock last week. He still has the expansion plugs, and the check ball it self. 
I'll try using some carb cleaner on mine and see if I can get things moving with out taking it apart. 
I still think I can make new seat cover plates, just need a "take out" that isn't to badly damaged.


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## Eccentric (Sep 12, 2011)

Sawchips said:


> No Joy on the check ball assembly.
> Bob says someone from California bought out his remaining stock last week. He still has the expansion plugs, and the check ball it self.
> I'll try using some carb cleaner on mine and see if I can get things moving with out taking it apart.
> I still think I can make new seat cover plates, just need a "take out" that isn't to badly damaged.


 
Wasn't me. I swap 'em out for Tillotsons. I _had_ thought about getting a couple sets to rehab the flatbacks sitting on my shelf though. It was a low priority....


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## Sawchips (Sep 12, 2011)

Eccentric said:


> Wasn't me. I swap 'em out for Tillotsons. I _had_ thought about getting a couple sets to rehab the flatbacks sitting on my shelf though. It was a low priority....


 
We'll let you off the hook  you were the first person I thought of. 

The culprit was working on a 660, Bob thought.


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## Eccentric (Sep 12, 2011)

Sawchips said:


> We'll let you off the hook  you were the first person I thought of.
> 
> The culprit was working on a 660, Bob thought.


 
Ha!

I figured I'd be a prime suspect. I don't have a 660 either (although I DO have a 650 that's now Tillotson HL63 equipped). I think I know who it might be......as he is in ca and owns at least one 660. It's not who you think either. Not gonna give him up however...


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## Sawchips (Sep 12, 2011)

Eccentric said:


> Ha!
> 
> I figured I'd be a prime suspect. I don't have a 660 either (although I DO have a 650 that's now Tillotson HL63 equipped). I think I know who it might be......as he is in ca and owns at least one 660. It's not who you think either. Not gonna give him up however...


 
No need to rat him out......not yet anyway:msp_smile: I ran some carb cleaner through it tonight. That changed the ball color from a gooey looking black snot to a clean off white color, and it now moves freely. Also got a good stream of cleaner through the venturie booster while spraying through the seat orifice. Should be good to go. I forgot to take pictures tonight, but I'll make sure to get some during reassembly, and then post them. I'm sure it will help the newbie's that find this string.


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## arrow13 (Nov 15, 2012)

*Mac CARBS*

Great info to use for my saws. Thanks everyone for putting your wisdom and humor into this.
Will:msp_biggrin:


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## mcc 86 (Feb 26, 2013)

*great info*

Hey Mark. just wanted to let you know, and everyone else who has contributed to this thread a great thank you! This is just the kind of info i love to see. (very informative and attention to detail) I could defantly use this info. Thanks again!

Aaron


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## jerrycmorrow (May 29, 2013)

great thread youse guys. subscribing and bumping


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## Frank Boyer (May 30, 2013)

I have a 1-86 carb that I need to work on. The primer doesn't work.


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## heimannm (May 30, 2013)

Other than replacing the external O-rings between the primer and the carburetor body, there is not much that can be done with the primers. 

Start searching e-bay or any other parts suppliers you may know of to see if you can locate a new one. There are a few out there still. I have seen them go anywhere from $5 to more than $15 on e-bay.

Mark


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## Frank Boyer (May 30, 2013)

Thanks


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## Eccentric (May 30, 2013)

The last two NOS primers that I saw on feebay (from the same seller) went for $25 and $50. Frank I may have a good used one for you. I take it the NOS HL103 thing didn't pan out. If that deal does come through I'd still be down for at least one.:cheer:


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## Frank Boyer (May 30, 2013)

He only had one and it was $60 plus shipping.


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## FergusonTO35 (May 30, 2013)

On the subject of Mac carbs but way smaller, I just rebuilt the Zama M7 on my Mac 160S. Anyone know the suggested initial settings for it? It starts and runs but I'm having a heckuva time getting it to idle without the chain moving.


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## heimannm (May 30, 2013)

In general I start with the low 1-1/4 to 1-1/2 turns and the high 1 to 1-1/4 turns open from lightly seated.

If the idle speed is correct and the chain is still moving it could be a failing bearing in the sprocket/drum, or that the clutch springs are just weak and worn out.

Mark


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## FergusonTO35 (May 30, 2013)

Thanks. I ran it some more after work and it looks like the clutch is the problem. It starts, idles, and cuts great. You can turn the idle up and down no problem, you just can't run it slow enough to keep the chain still. I know everyone hates these things but when its running well this little Mac is one of my favorites. At one point I had six of them, I think I could take one apart and put it back together in a coma.


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## burl1984 (Feb 13, 2014)

I have a 1/72 BDC 14 mounted to a high rise manifold which is supposed to fuel a SP125C/101b modified saw. I think I have rebuilt it completely but can't get it to fire up. I replaced all the parts the way the old ones came out but now I'm thinking the original carbutetor build may have been incorrect. Can somone post a link to a pictoral sequence for rebuilding a BDC14 please? I can get the saw to pop and run for a short while by putting some fuel down the bore of the carburetor but it doesnt seem to want to pick up fuel. I pulled the clear fuel line off and pulled the starter cord over several time and it seemed as iff the fuel pumped back out the fuel inlet fitting on the carburetor instead of sort of into the fitting. Could it be that the pupming mechanism is reversed inside? I'm relativly new to the McCullochs and have basically been builing this saw from lurking on the Karting forums and this site. The tank is a custom aluminum tube mounted infront of the BDC14 like most of the youtube videos show of the modified 101b saws. 

Any help would be greatly appreciated.

Thanks,

Burl


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## heimannm (Feb 13, 2014)

I have an IPL for the BDC14, send a "conversation" with your e-mail address and I can forward a copy. Those carburetors have a duck bill valve and some additional circuit plate diaphragms and gaskets, plus a different metering diaphragm than the standard flat back carburetor (66092 vs 55067 used on the saw carburetors).

Mark


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## burl1984 (Feb 13, 2014)

heimannm said:


> I have an IPL for the BDC14, send a "conversation" with your e-mail address and I can forward a copy. Those carburetors have a duck bill valve and some additional circuit plate diaphragms and gaskets, plus a different metering diaphragm than the standard flat back carburetor (66092 vs 55067 used on the saw carburetors).
> 
> Mark


I purchased all new circuit plate gaskets 1 thicker and 1 thinner and the circuit plate diaphram really thin. The Duckbill was also replaced at the same time. I purchased the kit BDC14/16 from marmax's karts and parts ca. I actually bought 2 kits because in the long process I have been taking to build a saw for the local competitions I have accumulated almost enough parts to build two saws. If i happened to ruin any of the soft parts a can just harvest them out of the other kit.

I'll pm you with a personal email.

Thanks Mark!

Burl


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## heimannm (Feb 15, 2014)

I have tried to add back all of the missing photos, hope this helps some of you with the MAC carburetors.

Mark


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## SEAM (Feb 15, 2014)

I have a number of these flatback carb Macs with dead primers... I use a sheet of copy paper covering the carb bore as a choke to start them. Works perfectly.


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## heimannm (Feb 15, 2014)

Creative solutions abound!

Mark


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## burl1984 (Feb 15, 2014)

heimannm said:


> I have tried to add back all of the missing photos, hope this helps some of you with the MAC carburetors.
> 
> Mark


Mark, 
Thanks for the IPL. I checked my rebuild job on the bdc14 carb. The only difference that I could tell between the IPL and my build was the rotation of the duckbill valve. The one that was in the carburetor originally was basically goo. I put a new one in but was about 90 degrees out from what the IPL shows. I'll report on conditions soon.

Thanks,

Burl


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## burl1984 (Feb 15, 2014)

I got everything re-assembled and didn't have to dump raw fuel down the carburetor to get it to pop. I saw somewhere while lurking that 1 turn out on the Low and 1.5 turns out on the High would be a starting point for the carburetor needle settings. I did a little adjusting on the low to add some more fuel because it kept dying. But at least for now i'm better off than before. Just in case anyone is wondering the carburetor I'm using is not the chainsaw model flat back, it is the MC 91-93 kart engine petrol carburetor w/o the pop off settings or the high idle setting. I did purchase an oem choke plate, arm, spring and detent ball to make it easier for starting.


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## burl1984 (Apr 27, 2014)

I tore down the saw and realized that I had in fact already installed the lower compression model head per Terry Ives advice. I did notice though while I was loosening the head bolts that they seemed rather easy to loosen. Does anyone use loctite on the 101b head bolts? I re-torqued them and set the lever height on the nos carburetor at the height of the housing. I'll report back this afternoon.


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## burl1984 (Apr 30, 2014)

I got the saw to Idle! I'm still not able to throttle up though. I rigged up the throttle with a section of stainless tig add rod and every time I attempt to throttle the saw ot adjust the high needle from the lightly seated position the saw shuts off instantly. I'm not sure if it's getting too much fuel during those times or if it gets too much air to fuel ratio and shuts off. Either way my investment is starting to pay off!


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## burl1984 (Apr 30, 2014)

Here is a video of it running but it's more like an audio clip, it got dark on me after work. But I'm glad it's running!


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## burl1984 (May 9, 2014)

Here it is throttling up. I'm going to take it to a local shop to have them help me tune it better and possible build a better cone pipe.


I think the previous BDC14 that I had installed on it was modified for Alky and was just getting way too much fuel.


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## heimannm (May 9, 2014)

Nice to hear it run, congratulations on your perserverence.

Mark


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## Sean McCarley (Jun 25, 2014)

this link helped me out very much. after i rebuilt my carb in my 895 it wasnt getting fuel, then i took it apart again and put the diaphram on the bottom and one gasket on top and it ran like like a boss. thank you very much marc for helping me out here


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## ilikeurtractor (Jun 2, 2015)

Great post guys - thanks for taking the time to document. I picked up a McCulloch 380 with a flat back carb a couple of months ago and it refuses to pump fuel. If I take the pick-up tube out of the fuel tank and fill it manually while keeping it vertical it runs and idles like a champ (gravity feeding the carb). If I run clear tubing from the carb to a small jar of fuel below the saw it will only make bubbles when I turn the engine over (spark plug removed for ease of turning the motor over). So I'm guessing it is either the diaphragm for the pump or a check valve. Reading this post there seem to be talk of a check ball and spring under one of the welch plugs but I can't find specifics of what this check ball may do or if it's even there for sure. I'd hate to remove the plug(s) to not find anything. I'm going to start with a new diaphragm but if that doesn't work I'm not sure what to go to next. The existing diaphragm seems a little stiff compared to the rest of the layer material, but I can't tell if it's stiff enough to not function. I suppose this would hold true for the "duck bill" checks as well which also seem a little stiff. I'll let you know what I find out after I change it. Any information on what's under the welch plugs and the function in the metering diaphragm (main carb body) would be great. Thanks again and I hope I can add to the post!


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## heimannm (Jun 3, 2015)

The check valve was only found on later versions, earlier one had a sintered metal "capillary seal", the purpose of either was for the high speed circuit flow control not the fuel pump.

Your case sounds like the fuel pump check valves on the diaphragm. Make sure the carburetor plates are clean and smooth where the check valve flap seal and that the flaps themselves are in good condition. I often find I can prime one directly down the throat of the carburetor and get it to start and run even when it won't pump fuel just by cranking it over with the rope.

Mark


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## ilikeurtractor (Jun 3, 2015)

Mine would "kind of" run on its own when the fuel tank was full. It was very difficult to start and wouldn't idle very long even at that. When the saw was hot, the fuel tank pressurized and it would run better. After my first use of the saw I set it down in my garage and it sounded like a leaking tire. I wasn't sure what it was until I realized it was coming out of the cork-type plug in the fuel cap. I hope the saw doesn't continue to run hot after I get the pump fixed and the mixture screws set slightly rich.


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## ilikeurtractor (Jun 3, 2015)

Here is a picture of one of the plates. Is the "capillary" sintered plug what I have shown in the picture? I also noticed a nick on the edge of one of the check flap holes. Hope this isn't my problem. If so, I'll try to seal it with some type of sealant.


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## ilikeurtractor (Jun 5, 2015)

Well I installed new diaphragms and I guess in the end it runs better, but still seems like it should be better. I first changed the fuel pump diaphragm thinking that would get it. Then I tried the pump test where I tried to pump through clear tubing from a glass jar of fuel a couple feet below the saw. That time it didn't even seem like it would do anything, not even bubbles. Hooked it up to the tank and was the same as before - wouldn't start or idle. Then I changed the diaphragm associated with the needle and seat. Same results. Then I changed the gasket between the carb and intake port and that seemed to have helped some. I did test the small intake port path that goes to the fuel pump by holding a small piece of tissue over it and cranking the engine. This helped me confirm the port wasn't plugged and was operating correctly by blowing the tissue. Didn't really notice much vacuum though, just puffs of pressure. Maybe that indicates the crank case is not sealed like it should be, but I'm not sure how well vacuum would work with the tissue test anyway.

But whatever problems still exist, if any, it will be good enough to cut the amount of wood I plan on using it for so I'm going to leave it as-is and move on. For a 40+ year-old saw I guess I can't have too high of expectations for it and it does run. The carb does seem "finicky" to adjust but this may be due to other issues affecting it. I did notice that fuel seems to spit out the throat of the carb when the saw is gunned when I had the air cleaner off for testing. I could feel it hitting my right wrist when I throttled it up. Not sure if that is normal or not. Maybe this indicates faulty reed valve(s)? I'll be glad when saws are fuel injected some day 

Thanks again for the post. If it wasn't for this I might not have messed with it much and I was able to learn a little bit amount along the way.


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## ilikeurtractor (Jul 29, 2015)

It turns out the root cause was the crankshaft seals were bad. I replaced those and now it idles fine. I have some other vintage saws that are exhibiting the same symptoms (having to constantly tune the carburetor to apparently compensate for air entering into the crankcase.) One is a Homelite C-series. Unfortunately, the flywheel seal on those is not easily accessed from the crankshaft side as the housing is integral with the crankcase. The McCulloch design made it easy to change seals. Hopefully I will be able to pull the seal from the flywheel side without busting down the entire saw, but it is a rather thin seal making it hard to use a seal puller on.


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## Eccentric (Jul 29, 2015)

Most saws are built like that (with the seal fitting into the crankcase casting rather than a bearing/seal carrier). Not many designs around with removable FW side seal/bearing carriers anymore. Also, the PTO side seal on both that Mac and the Homelite seat directly in the drivecase (C-series Homelite) and crankcase (large frame Mac).

The wandering tune isn't so much from the engine pulling air past the seal (although that can be a factor). More of the problem comes from a weak/varying impulse signal (crankcase pressure pulses) going to the pump section of the carb as a result of that leaking seal. The end result (wandering tune) and the root cause (a leaking seal or seals) is the same in any case....


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## ilikeurtractor (Jul 29, 2015)

Thanks for the clarification on the symptoms of a leaking seal. That is consistent with the saw not being able to pump fuel as I first experienced. I just got out of the garage and by some grace of God I was able to pull the seal out of the Homelite from the flywheel side. I drilled a couple of 1/16" holes in the face of the seal and was able to scoop it out with some dental hook tools. I really didn't think that would work like that. It showed me the seal was not very tight. The new one was similar and I put a thin coating of silicone around the outside perimeter before I drove it in. I'm not sure if that is a good idea or not but I'll take my chances if it helps seal things up. I greased the seal ID and shaft. I noticed that there is plenty of room in the seal area. I have a couple of C saws that probably will need seals and I think next time I'll just drive a new seal on top of the old and skip and chances of causing damage to the shaft or housing. I believe there is enough room. With some grease on the new seal and between the old one I'm thinking it will be fine. Breaking the whole saw down, pressing out the crank and then having to heat the flywheel bearing housing upon reassembly like the repair manual says just seems like a daunting ordeal to change a little seal out. They also say that when you heat the housing be careful not to heat it too much as you might damage the new seal. Wouldn't it be better to install the seal after heating, assembling, and letting it cool down? If the housing had a step in it so the seal couldn't come out the flywheel side then I could understand this but the bore is straight.


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## Bob95065 (Aug 1, 2015)

Where do you get the rebuild kits for McCulloch carbs? Can someone please post a link?


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## ilikeurtractor (Aug 2, 2015)

I found them on eBay but I see the seller (customchainsawparts) doesn't have any listed at the moment.


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## heimannm (Aug 3, 2015)

Contact Bryce (customchainsawparts) and he can get them for you. They are made by Joe Salva at Sugar Creek Supply but it is very 
hard to contact Joe.

Mark


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## Mastermind (Jan 23, 2016)

Bumping this thread to show my appreciation. 

Thank you Mark for an excellent and most informative thread.


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## sawfun (Oct 19, 2016)

I had to find the correct needle spring to prevent flooding. Mine needed a stiffer spring as there are several lengths and stiffnesses. Set the lever at .010 below the gasket surface and run 1/4" line to allow full flow for no delivery choke points. If you use the Custom Chainsaw kits on Ebay it should work well on a BDC 14 or 24.


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## BIGD4DICE (Dec 27, 2016)

heimannm said:


> While we are on the subject of governers, I also have a 740 with an air vane governer. On this saw the spring loaded air vane governer pulls the throttle open and a high speeds the air flow from the flywheel pushed the air vane closing the throttle. This is how it was done before the days of RPM limited electronic coils. Again the throttle linkage is not directly connected to the lever, but simply allows the spring loaded air vane to push the throttle open (or closed, depending on engine speed).
> 
> All together
> 
> ...


I have this carb on my 797. At idle after only 10 seconds it runs up and stays high idled with a pulse. Im not savvy to saws a lot but have heard it may be crank seal leaking. I'm taking it to saw shop in the morning for vac test. I don't have much for tools. Hopefully something simple. My second 797 and not having much luck. Has good compression. Will test it tomorrow too.


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## chy_farm (Jul 7, 2017)

heimannm said:


> View attachment 333664
> --------


All the contents here are very informative Heimannm, to me the most amongst them is this maximum velocity of rotation for stock 740. this information surely help me calculate another better pipe for that series. Thank you for sharing!
Chy


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## 2broke2ride (Jul 7, 2017)

Bob95065 said:


> Where do you get the rebuild kits for McCulloch carbs? Can someone please post a link?



These are also available third party from chainsawr.com he gets them from sugar creek supply. Cost about $30.


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## chy_farm (Jul 8, 2017)

Eccentric said:


> The 1965 Supplement to the McCulloch 1-40/1-50/1-60 series service manual describes both valve systems in detail, and instructs technitians to replace the older capilary screen type setup with the ball type check valve when servicing older carbs.


Hello Eccentric, thanks to your tip I was able to find this information at the other site, CSCF. It will help me a lot in tinkering this old carb.
Chy


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## Wojoe51 (Nov 13, 2018)

stinkbait said:


> Been fighting witn the same crap on my mcculloch 440. i just gave up for a while I'm sure that I will get back to it one day. I bought the sugar creek kit and the kit from discount marine, and no luck.


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## Wojoe51 (Nov 13, 2018)

stinkbait said:


> Been fighting witn the same crap on my mcculloch 440. i just gave up for a while I'm sure that I will get back to it one day. I bought the sugar creek kit and the kit from discount marine, and no luck.


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## Wojoe51 (Nov 13, 2018)

Does anyone know about the primers on the 440s? mine is leaking fuel around the plunger when running - to me if it leaks fuel it can leak air - Seen the name Bob Johnson regarding these but cant find him...
any help would be appreciated


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## Chainsaw Jim (Nov 13, 2018)

Wojoe51 said:


> Does anyone know about the primers on the 440s? mine is leaking fuel around the plunger when running - to me if it leaks fuel it can leak air - Seen the name Bob Johnson regarding these but cant find him...
> any help would be appreciated


You can remove the primer pump to service it. You likely need to replace the two little o rings and you're good to go.
It's a simple design and easy to work on.


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## heimannm (Nov 14, 2018)

The primers on the large flat back carburetors are non-serviceable. Your only option is to find someone with some NOS ones, or just plug the ports and prime it manually down the throat for cold starting.

The primers on the 10 Series are serviceable, but there are 5 or 6 different versions and you need to know how your is to be configured.

Mark


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## Wojoe51 (Nov 18, 2018)

heimannm said:


> The primers on the large flat back carburetors are non-serviceable. Your only option is to find someone with some NOS ones, or just plug the ports and prime it manually down the throat for cold starting.
> 
> The primers on the 10 Series are serviceable, but there are 5 or 6 different versions and you need to know how your is to be configured.
> 
> Mark


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## Wojoe51 (Nov 18, 2018)

Mark - U mentioned getting a primer from Bob Johnson - I cant seem to locate him on this forum - U got any info on how I could contact Him??


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## heimannm (Nov 18, 2018)

Bob only works by phone 607 638 9297 Eastern time zone.

Mark


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## Wojoe51 (Nov 18, 2018)

thank you very much


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## Wojoe51 (Dec 17, 2018)

Anyone know where I can get a needle and seat for mac flatback carb???


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## heimannm (Dec 17, 2018)

The seat is not a replaceable item for the carburetors used on saws, the kart carburetors used on the 49, 90, and 91 had a replaceable seat. 

The needle used with the replaceable seat is 63038 which I believe is the same as the one used on the saw carburetors without the replaceable seat even though the part number is different (83753 and 87875). 83753 is also used on the MDC carburetor on the Mini Mac saws. 

The needle itself is 9/16" long (.562) and has a rubber or Viton tip.

I have some extra needles (used) and a few of the kits with new needles and the metering levers for both the MAC and BDC carburetors; kit part number is 85059 and someone had written the 63038 part number on the package which leads me to believe they are all the same.

Mark


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## heimannm (Dec 17, 2018)

After looking through some carburetors I have I find some that were removed from saws do indeed have a removeable seat like the kart carburetors. It seems my McCulloch Carburetor Guides are not entirely comprehensive in covering all the carburetor options.

Mark


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## heimannm (Jun 21, 2021)

Bump


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## mirage (Jul 15, 2021)

I got a rebuild kit from Bob for my Mac 250 . Got the two 0-rings for the primer also. Still can't get it to start when it is cold. About how many pumps does it take to get the saw to start?


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## heimannm (Jul 17, 2022)

Updating an old thread. Thanks to Parker Jameson (I don't remember the screen name he uses here) I was inspired recently to look into rebuilding some of the primers used on the large McCulloch saws with the MAC/Walbro carburetors.




As others have also observed, the primers tend to leak after a while and often stop pumping as well making the saws hard to start. I had tried a number of times to pull them apart, even tried threading the hole in the end of the plunger to use a small slide hammer but I was never able to get one apart. Someone told me Parker had come up with a solution so I contacted him and he freely shared everything he had learned.

To get the primer apart, the key is to drill a hole in the back end directly in the center, and press it apart. He used a 3/16" drill but I went slightly smaller so I could tap it for a 10-32 set screw to seal it back up when the work was complete.

Parker recommended using a 1/2" drive socket to hold the primer which work perfectly with the 1/2" square aluminum body of the primer. Be sure to drill the hole dead center so you can press squarely on the plunger to get it apart.




Parker's press set up using a vise.




I made some special tools for this project starting with this to work in my small arbor press. I made a few modifications to the press a while back including drilling a 3/8" diameter hole in the center of the ram to serve as a tool holder. I used a short section of a #25 drill bit for the punch portion and made the body long enough that I could grip it with a pair of pliers to give it a twist as needed when I pull it out of the ram.




Once the primer as been pressed apart you can see the simple arrangement inside. Since this was not intended to be a serviceable parts there are no official names or part numbers for the components so I have applied some for the sake of clarity. There is only one o-ring used in the location shown, and the cup or v seal has completely disintegrated into tar.




When I disassembled several primers for rebuilding I noticed two different plungers (one steel, one aluminum) that utilize two different cups or v seals.




Digging through my assortment of McCulloch parts I found two different cups / v seals that were apparently the same as the ones used in the primers. Both of these are used in the manual oilers on different front tank saws. 24104 matches up with the cup on the aluminum plunger and 67116 matches with the cup on the steel plunger.




After removing all of the old deteriorated cups and o-rings it is time to reassemble. As I mentioned, I tapped the back of the primer body to accept a 10-32 set screw, Parker has the ability to weld aluminum so he simply welded the body closed. 




The cup, 1 o-ring, and gland installed on the aluminum plunger.




It is important to get the gland pressed in to the correct depth in order to achieve a good seal with the o-ring (after all, the main reason to go to all this effort is to stop the leaking...). Too deep and the o-ring between the gland and the retaining ring will roll back a forth, not deep enough and the o-ring will be compressed and will prevent the plunger from operating freely. To achieve this, I made special arbor tool to seat the gland in the correct position.




To be continued...

Mark


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## heimannm (Jul 17, 2022)

Ready to press the plunger into the pump body.




Done




I made another tool to press the ring in place flush with the primer body. Here you can see the o-ring tucked into the primer body, the ring in position, the the tool used to press it home.










After assembly, I work the plunger on the primer to make sure it move freely, some of them can be a bit sticky at first but it seems like 10 cycles or more and they work freely. I use a little air tool oil on the rubber parts as I am assembling the primers. Once I am convinced they work freely, I install the 10-32 set screw in the back with some red LocTite to make sure they stay sealed.




I wanted a simple way to test the primers before and after servicing, before to determine if they are operable and/or leaking, and after to insure proper operation. I had an old carburetor body on hand without the throttle shaft so I simply added a nipple to supply pressure and plugged the fuel passage. You can see that this one was certainly leaking before the rebuild.




After rebuilding I used a container with SeaFoam for testing, the SeaFoam seems to have a little oil in it and does not stink up the shop like using mixed fuel would.

No leaks.




I didn't attempt to make a video, but you can see the stain on the shop towel from the primer pumping fuel. They move quite a lot in a few pumps one they are primed.




Mark


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## heimannm (Jul 17, 2022)

The aluminum plungers with the 24104 cup seem to be a near fool proof repair. The steel plungers with 67116 cup caused me some problems...one would pump but would not hold pressure (leaks through the primer discharge port) and the other would hold pressure but would not pump. Because the dimensions are different you cannot use the 24104 on the steel plunger. I replaced the cup with a #010 o-ring on the non pumper and now it pumps, but still leaks through the discharge port. Conferring with Parker he noted that using a slightly stiffer spring for the check valve in the carburetor body would correct that. Ideally the primer check valve will but just slightly higher pressure than the carburetor pop-off setting but not so high that it make the primer hard to operate. H located some Tillotson HL metering springs that are just the right pressure so I have them on order now. For those that may not be familiar with the check valve, it is just a spring, check ball, and the same rubber seat as use in the Tillotson HL carburetors. I use #010 o-rings to seal the primer to the body of the carburetor.







Once I receive the new springs and do some additional testing I will report back.

Mark


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## Maintenance supervisor (Jul 17, 2022)

Im not trying to be smart Mark but is one port feed and the other prime out put? 
I was wondering if it would be possible to put brass nipples in those and use a primer bulb?


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## heimannm (Jul 17, 2022)

The blue port is the inlet coming from fuel channel connecting the fuel pump to the metering section and will be under fuel pump pressure when the saw is running.

The red port leads to a passage downstream from the venturi that directs the output from the primer into the intake of the engine. There is a check valve (ball and spring) in that port to ensure the output from the primer is discharged and not simply drawn back into the primer when the spring returns the plunger. This is a true primer that puts a charge of raw fuel directly into the intake.

The body of the primer provide enough resistance to prevent the fuel pump from forcing fuel past the check valve into the engine which would upset the mixture, or leaking past the primer when the engine is stopped which would lead to flooding while setting. Parker had this experience during his early modifications which lead to the search for the higher pressure spring for the ball check valve.

_I think the issues with the modern bulb type "primers" is they would not have the needed resistance and would allow fuel from the pumping section to be forced directly into the intake, and the amount of fuel that is displaced by the bulb type primers is so great that one actual discharge cycle would badly flood the engine.

This_ is all speculation on my part...

Mark


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## SawTuner (Jul 18, 2022)

Awesome write up Mark.
I have bench tested the primers before putting them on the carb and have had them hold well over 30 psi, testing from the fuel inlet port. The o-ring that goes in before you press the gland in needs to be just passed the inlet fuel hole in the primer body. You can see it as you are pushing it all together. If it is not passed the inlet hole I have found they will not hold pressure. 
Hopefully this all makes some sense
Thanks
Parker Jameson


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## Alaskan Stihl (Jul 20, 2022)

Eager Beaver Carburetor Issue:

So, it was my fault in regards of creating this catastrophic situation….

I am in the process of getting this McCulloch Eager Beaver back in running condition. After disassembly of the carburetor (Walbro MDC), I discovered that the Metering Lever clearance was too low.

So…you got it…I tried to lift it up a bit and it fractured and kinked the Forked End that slips into the needle valve.

Of course, none of the rebuild kits that I found on eBay comes with the Metal replacement lever.

Luckily, I have a stack of spare carburetor parts that I inherited. I dug through the pile and discovered the previous owner had several levers…which appear to be of aftermarket” construction.

I tried to fit in one of these levers, however it is too wide to fit into the recess area, however…looks like I might be able to file down both sides a bit and get it to fit correctly ….and luckily, I have several of these levers at my disposal so for trial and error until I get a modified one to fit properly.

Question: Has anyone attempted to use this type of lever and modify it to fit (see picture)?


Thoughts?
Alaskan Stihl


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## heimannm (Jul 22, 2022)

Metering lever is on the way to Alaska...

I went through another batch of primers yesterday/today, it can take a long time to clean all of the old, decomposed rubber rubber from all of the working parts.




This time around, the two with the steel plungers (use 67116 v-seal) only needed o-rings, the v-seals were still fine. I did use an 010 o-ring in place of the v-seal on the first batch and that works as well.

As Parker mentioned, getting the gland pressed to the correct depth is important to ensure the plunger presses firmly against the o-ring to create a good seal when the plunger is pushed back by the spring. This will allow the primer to hold back the fuel pump pressure when the saw is running and prevent fuel from leaking past when the saw is setting, especially when warm which would lead to flooding.

With my new special tools the job went fairly quickly getting all the primers apart. 

First, I modified a 1/2" deep socket by adding a set screw to lock the prime in place while drilling the pilot hole in the end. Just FYI, even cheap Menards sockets are very hard and tapping for the 10-32 set screw is quite challenging. There is a lot of variation in the dimension of the 1/2" square aluminum stock they used to make the primers so I put a shim opposite the set screw, some .003, some .005, some .006" to try and keep the hole centered




I used a small center drill in a drill chuck in the tailstock to make the pilot holes, then switch to a peck drill with the correct size bit to tap for the 10-32 screw to plug the hole. The center drill won't wander when you start the hole keeping it centered on the body of the primer and the peck drill provides very good feel as the drill goes through so you can avoid damaging the plunger or spring if you go too deep.




Disassembly as before - press the primer apart using the socket to hold it and provide clearance for the plunger to come out.




I did not take a photo but I just chucked a tap in the peck drill and tapped the hole by rotating the lathe chuck by hand, I tried to gauge the feel of the tap and not cut the threads full depth all the way through. This way the set screw will seat in the fairly thin body quite securely, the addition of a little red LocTite makes it quite leak proof.

I did notice that the springs were not all alike, some are LH wound and some are RH wound. There did not seem to be any consistency to which ones had which spring (steel plungers were all LH, some of the aluminum plungers were LH but most were RH).




And finally, while most of the carburetors had a primer discharge port in the bottom of the throttle bore, at least one version (61857) discharges through the impulse port.




And before I forget, a 005 o-ring will make a good substitute for the square o-ring on the H and L adjust needles if the originals have lost their grip.




Mark


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## SawTuner (Jul 23, 2022)

You've got quite the pile of primers going there!


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## 2broke2ride (Jul 23, 2022)

heimannm said:


> Metering lever is on the way to Alaska...
> 
> I went through another batch of primers yesterday/today, it can take a long time to clean all of the old, decomposed rubber rubber from all of the working parts.
> 
> ...



Do you intend to offer the rebuilt primers for sale or perhaps on an exchange basis? If so, I would certainly be interested in at least a couple. 
I have a few flatbacks that I would be running if I had working primers. The choke flatback in my Super 250 runs quite nicely. I swapped to a Tilly in my 550 due to an inop primer and I have a 450 on deck.


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## heimannm (Jul 24, 2022)

That is my intent Kevin, sell outright or offer a discount on an exchange basis.

PM me if you would like to know more.

Mark


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## MacAttack (Jul 25, 2022)

I know this contributes little / nothing to the conversation but it's fascinating to me that McCulloch ever used a complex primer system instead of a simple butterfly choke like most every other small engine before the primer bulbs appeared... do I have that correct? A primer in place of a choke?


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## heimannm (Jul 25, 2022)

McCulloch wasn't the only saw manufacturer to build in an actual primer (not just the purge bulb like the modern saws) to put a charge of fuel either into the intake, or on some models directly into the crankcase to assist in cold starting. Everyone was looking for a reliable, easy starting saw and when they work properly the primers will provide that. 

Mark


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## MacAttack (Jul 26, 2022)

It actually makes a lot of sense, nothing gets a saw firing quicker than a shot of fuel straight into the crankcase or cylinder.

Especially if a saw has been sitting a while, there's nothing fun about having to get the carb primed up again.

Cool stuff.


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