McCulloch Pro Mac 10-10 Chain Saw stopping problem

cobrabobDecember 30, 2007

I have a Pro Mac 10-10 that is old but has always run when I needed to trim some trees or limbs. I bought it in 1979. Last year while cutting some trees it started sputtering and quit. After some minutes it would start again but sputter and quit. Since then I have cleaned the carb in carb cleaner solution. I have purchased a new ignition module (from company that bought all McCulloch parts when they went out of business) and installed a new plug. I have adjusted the carb per the owners manual I still have. I just cannot give it up. You need compression, ignition, and proper fuel mixture. What am I missing. It has been a great little saw and I want to fix it. I was thinking the spark plug might be defective and opens when the engine head gets a little warm. I have not pulled the engine completely down and looked at rings etc. I believe it is a Welbro carb (if that is the right name). Can any of you small engine experts help me. (I know the obvious answer is get a new saw!)

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canguy(British Columbia)

Typical for old Macs. Sorry, I could not resist that shot. You need to troubleshoot systematically instead of throwing parts at it. Remove the muffler and have a look at the piston. Is it showing any scoring or galling? Are the rings free in the grooves? Next is ignition. You say you replaced the module. That saw should have points and a condenser behind the flywheel, they are likely very worn.
Squirt a little gas, NOT starting fluid, down the carb throat. Does it fire then quit? Check the fuel line. It should be firm but not hard. If it is very spongy or hard and brittle, replace it and the in tank filter.
That saw has served you well for almost thirty years. I would not spend a lot of time or money on it as parts are near impossible to find and Macs were not overly reliable to begin with.

    Bookmark   December 30, 2007 at 2:36PM
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Two more things I can think of: the muffler is plugged with carbon or the vent in the gas cap is plugged. A plugged vent will let the saw start but will starve it of fuel after a minute or 2.
Did you replace the carb diaphrams & gaskets? Carb kits are inexpensive.

    Bookmark   December 31, 2007 at 6:19PM
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You should know it you getting spark with the spark plug removed grounded against the head, either it will spark or it won't have a pretty blue spark, then I suspect would igntion problems when it dies. Next you should know if it gets gas by priming it when it don't start. If you prime it and it fires off the gas or spary carb. cleaner. ( I like using carb cleaner it's safer and you get a side benifit of the cleaning action).

Providing the spark plug is good and you have proper compression I suspect it sucks air when it quites. I would replace all the fuel lines. this happens to most old saws IMO the inability to pull the gas to the carb. due to air leaks in the fuel system. Other possible guess is the little dodad in the carb that alows gas to flow with the spring attached thats a real ##th to get back togather.

    Bookmark   January 1, 2008 at 10:25AM
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canguy(British Columbia)

LOL That little doo dad is the inlet needle and it and it's bore get gummed up with varnish. If that saw has a Tillotson or Walbro carburetor the kits are readily available. If the early Mac carb, forget it.

    Bookmark   January 1, 2008 at 11:14AM
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Cobrabob": Since you still have the manual for the Mac 10 does it give you
the spark plug gap. I lost my manual some years ago when my
sons 'borrowed' the saw for some work and have since forgotten
the gapping of the plug.

Thanks for any help.


    Bookmark   July 5, 2009 at 11:49PM
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canguy(British Columbia)

.025" will work on most engines.

    Bookmark   July 7, 2009 at 7:57PM
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I just bought one of these at a garage sale. So far it's working great, but I don't have a copy of the user manual. Could you do us a great big favor and scan and post the manual?

At the very least, can you tell us the correct gas to oil ratio?

Thanks so much!

    Bookmark   July 26, 2010 at 3:31AM
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CG may have Onsite Manual Info ? As far as the Fuel Mixture back in the late 70's most saws were at 32:1 Ratio. Regardless use a Premium Oil and mix a Gallon @ 40:1 . Warm the Saw up and then make a few cuts and check the Plug Colour . Also take note of the exhaust , a little smoking is ok . Excessive to the point that the Plug becomes dark brown would indicate that 50:1 may be better suited to your older saw with the New Oils. I have a few 60's Vintage that I run at 70:1 with Amsoil . My New Husky and Stihl I run at 50:1 . The worst thing with older saws is to carbon foul the piston and rings .

    Bookmark   July 26, 2010 at 1:08PM
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