Hello...Pro Mac 55

[SierraMtns]

Update: The cap steal leaks just a very small amount when I tip the saw on its side. So I think its the vent. Its a very small amount so I will worry about it after the saw is back up and running.

The masker gasket kit is on its way. I took the carb off to check out the piston. Man does it look good.

The base gasket got ripped while removing the carb. Should I rebuild the carb while it is off? The saw started but I didnt cut anything with it.

I found a used 20" sprocket nose bar. Dose anyone know how many link chains the chain needs to be?

 

[a. palmer jr.]

If it's a 3/8 chain it would take 70 links for a 20" bar.

 

[heimannm]

You will get a new gasket for the base of the carburetor with your master set from ebay. It never hurts to take the carburetor apart for a good cleaning and to make sure the diaphragms are still pliable.

Note that your carburetor has a fixed "H" jet so you only have the ability to adjust the "L" circuit.

Mark

 

[SierraMtns]

What is the other screw if there is only "L"? Is the ideal screw? Why would McCulloch not put a "H" on these carbs?

Where do you order your carb kits?

 

[SierraMtns]

Is this the right kit?

http://www.ebay.com/itm/GENUINE-OEM...OR-HOMELITE-/281911528227?hash=item41a33c8b23

 

[heimannm]

That is the correct kit for the Walbro SDC carburetors.

The screw closer to the throttle is the idle adjust, that screw actually passed through the body of the carburetor and touches the throttle plate to hold it open. The other screw near in inlet to the carburetor is the "L" low speed adjustment

I believe there were too many folks leaning the saws out so McCulloch sold quite a few with the fixed "H" high speed jet. For most carburetors there were several different options for the size of the fixed jet.

I have a very similar carburetor on one of my SP125's and while it is very rich out of the cut, it pulls very well once you start to load up the engine. My other SP125 has been fit with one of the larger bore SDC's and is fully adjustable; you can certainly tell the difference in performance. I use one only as a cookie cutter, the fixed jet saw frequently goes out for work.



Mark

 

[SierraMtns]

That is the correct kit for the Walbro SDC carburetors.

The screw closer to the throttle is the idle adjust, that screw actually passed through the body of the carburetor and touches the throttle plate to hold it open. The other screw near in inlet to the carburetor is the "L" low speed adjustment

I believe there were too many folks leaning the saws out so McCulloch sold quite a few with the fixed "H" high speed jet. For most carburetors there were several different options for the size of the fixed jet.

I have a very similar carburetor on one of my SP125's and while it is very rich out of the cut, it pulls very well once you start to load up the engine. My other SP125 has been fit with one of the larger bore SDC's and is fully adjustable; you can certainly tell the difference in performance. I use one only as a cookie cutter, the fixed jet saw frequently goes out for work.

View attachment 570996

Mark

Well thats great news. I was worried that I was going to have to start looking for a different carb with the "H" screw. I always keep my chains sharp and dont mind turning up the "H" screw a little but if you say it cuts good in the cut I will just run it.

PS....That SP125 is sweet. Hope to run one someday.

 

[SierraMtns]

Has anyone tired a fuel line form a McCulloch 250? I got a couple boxes of parts from a local guy and found a 250 fuel tank with the line still attached. The line was dry rotted and broke but I was able to try it in the PM 55 tank and it fits a lot tighter.

The line looks a little bigger too. Anyone have part # for these lines?

250 fuel line is on the right.

 

[SierraMtns]

The 250 line looks like this one?

http://www.ebay.com/itm/Fuel-Line-M...870588?hash=item1c743760bc:g:rAsAAOxyOlhSsIWG

 

[heimannm]

Someone McGyver'd your 250. Standard setup from the factory would have been a barb on each side of the tank (one inside the tank, one outside the tank) with the fuel line in 2 pieces.

The original fuel lines from the tank to the carburetor were a very large O.D. to fill the hole in the air box where they passed through, on later ones the fuel line was molded more like the one you have shown with the built in grommet filling the hole in the air box. There would always have been a separate line in the tank with the filter.

Large O.D. line passing through the air box to the carburetor



Line with the molded grommet for the air box - the line you see here connects to a barb fitting external to the fuel tank, with another barb fitting internal with the separate fuel line with the pickup.



Mark

 

[SierraMtns]

Someone McGyver'd your 250. Standard setup from the factory would have been a barb on each side of the tank (one inside the tank, one outside the tank) with the fuel line in 2 pieces.

The original fuel lines from the tank to the carburetor were a very large O.D. to fill the hole in the air box where they passed through, on later ones the fuel line was molded more like the one you have shown with the built in grommet filling the hole in the air box. There would always have been a separate line in the tank with the filter.

Large O.D. line passing through the air box to the carburetor

View attachment 571286

Line with the molded grommet for the air box - the line you see here connects to a barb fitting external to the fuel tank, with another barb fitting internal with the separate fuel line with the pickup.

View attachment 571287

Mark

So do you think the one I posted from ebay is a larger OEM one?

http://www.ebay.com/itm/Fuel-Line-M...870588?hash=item1c743760bc:g:rAsAAOxyOlhSsIWG

 

[heimannm]

No, the e-bay one is strictly 10 Series that uses a different filter with a small barb to fit the fuel line.

Mark Heimann

 

[SierraMtns]

The PM55 fired right up.

The "L" screw is 1.25 turns out. And adjusted the idle screw to 2,650-2,700 RPM's with just a few puffs of blue smoke.

I ran it WOT for just a sec and checked the max on the Tachometer.....12,100 RPM WHAT?????


Since it doesn't have a "H". How can I turn it down? Or should I even be worried about it?

Im cutting down a big Digger Pine in a couple hours and want to run the saw.

 

[rwoods]

If it were a 82cc MAC I would say maybe a tad too lean. Don't know about the 55. Ron

 

[heimannm]

Bar and chain installed? Does it at least burble a little?

Mark

 

[SierraMtns]

Bar and chain installed? Does it at least burble a little?

Mark

It was no bar/chain.

Burble at idle?

How much does the "L" effect the high RPM's? Maybe I should back the "L" out another .25 turn just to be safe.

 

[heimannm]

Burble a little WOT, it shouldn't be running cleanly if the "H" jet is big enough to provide all the fuel needed under a heavy load. The "L" provides an very small amount of fuel and won't have a very noticeable impact on the high speed performance.

12,100 RPM with absolutely no load is not all that extreme. Put on the bar and chain and I think you will find it comes down enough to make it noticeable.

Mark

 

[lostone]

Thanks heimannm, for the info on the replacing of the duck bill in the caps. I have two Mac's (555 and 700) that are needing new valves. I ordered two of the Poulan valves since you said they require no moding in order to get them to work. I have already taken my caps apart and the old valves where nothing but black chunks inside. I bought a mityvac to test out my saws for restoring and this was the first test I used it on.

 

[lostone]

I would like to add an update to this, I used the Poulan Duckbill valves on my fuel caps and its working great.

I had ordered a NOS fuel cap to replace one of mine that had a large chip out of the side of it and the valve in it (the new one) had turned to goo about like tar, where the used ones had hardened and just came out in chunks. The springs in mine are a bit different then the springs you show in yours and are tapered, it requires the smaller end to be pointed towards the Duckbill valve in order to work correctly. I put the mityvac to them and they are working great now.



When putting pressure if I go to 7lbs it bleeds to 5lbs and holds. When pulling a vac. it zero's almost instantly,

 

[bgonzo]

It looks like you need a walbro K10-SDC carburetor kit ( I zoomed in and see SDC on the carburetor).
Replacement fuel lines are available aftermarket. I put a little teflon tape around the grommet to get a better seal on mine and they done seem to leak. Yours likely has a wick type filter, which works but when they get old they can fall apart.
I don't see anything missing on the exhaust. It looks funny without the chain brake but yeah, some didn't have one.
I run 35:1 ratio in all my saws, new or old. There are PLENTY of fuel oil ratio discussions here.


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I've been looking for an expert on these chain saws. I have an old Pro Mac 55, that I got from my Father years ago, and I know very little about. The saw hasn't been run in at least 30 years, and is difficult to start and keep running. It has a Walbro SDC Carburetor which is marked 7-74 49, which I assume is a date and a carburetor version. From this forum I've learned that it has a fixed high speed jet like the one in the photo posted earlier in the thread. I have a few questions about this saw.

1. Is K10-SDC. the correct carb kit for this carburetor?
2. Is it ever necessary to change the fixed jet to run better on the crappy gas we get these days
3. What is the procedure for adjusting the needle valve?
4. I'm assuming I should also order a new fuel line and filter?
5. There appears to be a small filter inside of the brass fixed jet. Does this need to be replaced?

Any more pointers about this saw? According to this forum, the Pro Mac 55 seems to be a popular saw.
Thanks in advance for your advise.