McCulloch Pro Mac 610 - Runs great but smokes like madness & fuel everywhere

[B.C.]

So I've been working on a McCulloch Pro Mac 610 for some time now, I've got her just about good, or so I thought. Long story short and leaving all the other stuff I fixed and trying to focus on just the pertinent - The carburetor seems to run fine and tune fine, but it smokes like crazy. Walbro HDB L1 carburtor. I have an Echo 500VL with very similar Walbro HDB L3 that smokes a bit when started but far, far less once warmed up for about 20-30 seconds. The 610 could fog a damn field for mosquitoes and warming does nothing. It spews so much smoke and unburnt gas that it covers the entire saw like dew in a pretty short amount of time making it wet, especially on the muffler side, it will drip off in some areas.

The carburetor was kitted with genuine Walbro kit including needle, all gaskets, and both diaphragms. Lever set EXACT to Walbro tool HDB side height. Tool just slides over lever with near zero gap. I did try it slightly higher and lower and there was no change.

Spark plug is called for DJ8Y - tried swapping with champion plug, runs same.

Compression tester maxed out at about 167 psi.

Swapped ignition coils with spare saw - no change.

Tuned L so low it is ready to stall - no significant change other than slower rpm and can't rev as high, still excessive smoke / gas/oil.

Brand new oiler from Bob - Genuine McCulloch part, dated 2000.

I see people running them in all kinds of videos with pretty much no smoke at all to be seen... :/

 

[s sidewall]

Try running it without any lube in the oil tank, bone dry.

Steve

 

[B.C.]

I see you have a PM605. I've about exhausted every thread I can find via google on smoking 610s. Best info I can gather is that they sometimes leak oil down into the crankcase and will smoke. Sounded like maybe it was only supposed to be for a while at startup but wasn't clear. I ran it today for at least a good couple minutes and it still was smoking like nuts while I was tuning the carb up. Was going to run it for a good 10 minutes tomorrow and see if it clears up despite knowing it would be absolutely covered in gas & oil. Was hoping maybe with as many folks that seem to have one of these 610s or similar model that someone would know definitively what was up. I see lots of 610 vids on youtube of guys starting them up cold with no smoke at all. Why can't mine run like that! haha.

Will try running it tomorrow with no oil as well, that's a good idea to test if it is burning oil. I was going to make a gasket to block the oiler but I guess it shouldn't hurt anything running it dry and that would be easier so I will try that as well and update.

 

[heimannm]

Did you replace the gasket and diaphragm in the automatic oil pump? If not, you will continue to draw bar oil from the tank into the crankcase.

Most 600 Series saws will clear up after a minute of run time or less if the automatic oil pump is working correctly.

Mark

 

[s sidewall]

Mine will smoke for about 30 seconds to a minute but I always let my saws sit and idle for a bit before I start using them.

Steve

 

[B.C.]

Thanks for the input guys.

Mark, I got a brand new genuine (old stock, appears to have date 00 on it, so I'm guessing 2000) oiler from Bob in Ny. I also ordered a new base gasket which helped seal it back to the crank nicely. It now oils good too, but smokes like a chimney. I haven't run it for more than 5 minutes yet or without oil to see if it clears up, will do both tomorrow. Think I asked Bob if he had any of the diaphragms but just the new oilers if I recall correctly so that's what I got, 2 of them. So are they bad right out of the package basically because they are so old then or something? That would be a shame, I bought 2 of them. (Also curious if those 19 year old ones are the newest you can find or if some aftermarket or something else exists, I looked but couldn't find anything.)

 

[Timdog]

They always smoke when you first get them work on them and let it sit and idle doesn't seem to do much what has worked best for me is to actually use the saw and cut some wood

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[B.C.]

Ok guys so I got it back out and after a bit of testing just now I think that maybe I DO have a fuel problem after all. I ran it for only a few minutes, maybe 5 at most yesterday and I had filled the tank about 2/3 full. Figured I probably shouldn't need to but I checked the tank anyway before I started running some more tests today. To my surprise it was nearly empty.

So I gassed it back up to about 2/3 full again, bout half way between 3/4 and 1/2 full (5/8 full I guess) and gave her a bit of run. I was mostly idling and then was throttling occasionally to see if I could clear the smoke. Oh btw I had drained the oil tank completely before starting today, that was a great idea to eliminate that variable Sidewall. Tried running for a while to see if the smoke would clear... It did not. After about 5 minutes or so I checked the tank and it was down quite a lot again about half way between 1/4 & 1/2 (3/8 full). That really seems like some insane fuel usage. So I'm pretty sure it's running SUPER rich at this point as that amount of fuel usage seems very, very high. (This makes sense too because the spray that comes out is more like gas than oil, it's not sticky like the bar oil is, it just wipes off like gas) It COULD also be burning bar oil but it seems pretty apparent it's DEFINITELY burning a crazy amount of fuel. I'm not sure how to fix that, it runs great and I have a new kit in it. The only thing I can think of to do is replace the little diaphragm check valve in there. I have a new kit in that carb, genuine walbro, and I have the lever set exactly at the height the walbro tool has on the side for hdb, which is flat/flush w/ the top, just a .005" below per manual spec. I did note in a manual I got from chainsawr that it mentions there is a governor that will make it run more rich if the rpms go too high. I don't know if that is what that little check valve diaphragm is for, and maybe it's not functioning is why it's running insanely rich. Only explanation I have other than just unknown/bad carburetor for whatever reason.

 

[Timdog]

Thinner gaskets in the new kits so you would have to adjust your metering lever to compensate

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[SteveSr]

I did note in a manual I got from chainsawr that it mentions there is a governor that will make it run more rich if the rpms go too high. I don't know if that is what that little check valve diaphragm is for, and maybe it's not functioning is why it's running insanely rich. Only explanation I have other than just unknown/bad carburetor for whatever reason.

These governors can get crud in them and even behind the spring and then allow direct bypass of fuel into the saw. Unscrew the governor and look for crud in the carb that would keep the check ball from seating. If you find any there is probably more behind the ball and spring. Cleaning gets interesting at this point as you have to depress the ball and simultaneously flush the area behind the ball with carb cleaner. An alternate idea would be to depress the ball and spring and hold it with some small (and soft) copper wire and toss it into the ultrasonic for a while with carb cleaner.

The only other thing to check is that the gasket and metering diaphragm are installed in the correct order. Usually the gasket goes under the metering diaphragm.

 

[B.C.]

I have referred to service manual diagrams (bought manual from chainsawr website today) for the gaskets and they are correct. According to the service manual the only carburetor that had a governor was the HDB-7A. It has a brass plug in the side I think. Mine does not. It is an HDB L1. I don't see a ball bearing in the diagram in the carburetor at all, or at the governor. There is a separate check valve however in both carbs, and I think all of the HDB type carbs, but I'm not sure what it does.

Have a second HDB-L6 from another mac 610 that I thought looked a bit corroded but I cleaned it up and slapped it on there a little while ago and it ran pretty much exactly the same. So that's 2 carbs that do the same thing. They are both very old of course and dated 78/79 respectively. Neither has had the little check valve replaced so I'm not sure if that is my culprit, if both have some other issue.

Side note: I turned in the L screw on the HDB L6 to see how far out is was, it was right about 1 1/4 turns where it should be. Runs good there, spits gas like mad. Both tuned and perform same.

 

[SteveSr]

I have referred to service manual diagrams (bought manual from chainsawr website today) for the gaskets and they are correct. According to the service manual the only carburetor that had a governor was the HDB-7A. It has a brass plug in the side I think. Mine does not. It is an HDB L1. I don't see a ball bearing in the diagram in the carburetor at all, or at the governor. There is a separate check valve however in both carbs, and I think all of the HDB type carbs, but I'm not sure what it does.

I am not specifically familiar with the HDB series. The ball bearing is part of the governor assembly. Above a certain RPM the ball bearing (check valve?) unseats and dumps more fuel into the venturi slowing the engine. The EPA would never allow that these days!

In any case it sounds like you have too much fuel getting into the engine. You just have to figure out how it is getting there. Leaking welch plugs are one place. You'll need a way to seal and pressurize the venturi to test this. A leaking main needle would be another. This can be checked by pressure testing the fuel line inlet. Should probably hold about 10 PSI.

There is also #13 in the attached diagram. I think it is just a fine mesh screen but can't tell without seeing it.

Side note: I turned in the L screw on the HDB L6 to see how far out is was, it was right about 1 1/4 turns where it should be. Runs good there, spits gas like mad. Both tuned and perform same.

Spits gas out the muffler or intake? If its spitting gas it can't be running good.

I bought a PM-610 as a cheap store return from Hechinger's in the early 90's. I used it extensively to clean up after a direct hit from hurricane Fran in 96. Once McCullough went belly up and parts started to become scarce I sold it and switched to Stihl and haven't looked back.

 

[Timdog]

I don't the 610 had a governor

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[B.C.]

Well I have another small update. Got the little check valve replacement kit in the other day, finally put it in today. No change. The check valve inside was quite stiff, but it made no difference. It still runs incredibly rich. I timed it today and it burns about 1/8 of a tank in around 6 minutes, with less than 10 seconds of full throttle, just let it sit and idle most of the time. Idle rpm is about 2000. It still spits quite a bit out the exhaust and it builds up on stuff. I let it run on a wood table and it makes a big black spot as it reflects off that top shield back down onto the table. Running same 40:1 I do in all my other saws.

I uploaded a quick video to see the smoke. I had run it for about 30 seconds before I started recording. Smokes a lot even at idle, hit the throttle and it just blasts out of there. (I still had no oil in the tank either and had run almost 1/2 tank of fuel through it already a previous day before I made my last posts, it's just running way too rich I think, not burning the chain oil.)

 

[SteveSr]

What is the result of the fuel line pressure test going into the carb? Will the carb hold 7-10 PSI?

 

[SteveSr]

Another thing... Others will correct me if I am wrong but I don't think you should really be running this in its too rich state as all of the extra gas dilutes and washes the lubrication off of the cylinder walls. Under normal conditions you have mostly gas vapor and a film of oil on the moving parts. The excess gas will wash this film away.

 

[B.C.]

I'm pretty sure i had done a pressure test on the carbs but I will verify that soon. (also have a 3rd carburetor on the way to try. Almost bought a good running 610 to try swapping carb on to but I missed it.) In the meantime, add this old girl to the list of saws I've personally had my hands on that run good, but extremely rich. I kitted this carburetor as well, it's got a Walbro SDC type. Runs pretty similar, idle good, throttle good, sprays gas like mad out the exhaust. Remington Woodsman.

 

[B.C.]

Pressure tested the two 610 carburetors. The spare leaks down very slowly. The one I have on there currently that I also did the check valve on held 7.5 psi for a full minute without budging.

 

[SteveSr]

Pressure tested the two 610 carburetors. The spare leaks down very slowly. The one I have on there currently that I also did the check valve on held 7.5 psi for a full minute without budging.

On the older carbs they used to spec a pop-off and re-seat pressure. To test you would pressurize the carb until it poped-off and then notice the gauge when it re-seated. The issue is that if the fuel pump pressurizes enough to pop-off or interfere with the re-seat then fuel effectively bypasses the metering mechanism and throws extra gas into the engine, possibly causing your issue.

With newer model carbs this isn't much of an issue. I have tested some that failed to pop-off at 20-25PSI and didn't leak down. So if yours actually leaked down and re-seated at 7.5PSI that might be an issue. I am not familiar with your particular model carb but @backhoelover might be if he is still around.

 

[backhoelover]

Need to go through carb and check Welch plugs, nozzl, also need to check adjustment needles and make sure that don’t have any wear. Also make sure carb doesn’t have a brass gov in it they work off vibrations I’ve seen they go bad and cause a rich condition. Also check your fulcrum lever height