McCulloch 10-10

rboone7760March 10, 2014

I have an old mac 10 that has not been used in years. It is probably from the late 60s or early 70s. I thought that it would be good if the old boy could run. The carb was rebuilt, new gas line and filter, new spark plug and fresh fuel.
The saw will now start and run. The carb has a low and high speed adjustments. When first started the saw runs really great with good response. After it runs for a few minutes the response is not good and finally stops. I thought that there might be a problem with the gas cap vent but when i opened it up that did not help, the saw was running then.
Does anyone have any suggestion what could be the problem. Thanks

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loger_gw

Suggestions:
1. Pull the muffler, check for carbon buildup/restriction. If it runs for minutes w/o slowing, this is probably not the issue. Ck cyl and rings for good surfaces while the muffler is off.
2. Check the compression cold, and then check it hot to see if the compression is affected.
3. Tweak the fuel mixture toward rich to see if itâÂÂs starving for fuel.
4. With an inline spark tester check the fire to see if it is maintained. Ck the points.
5. Good Fire/Fuel/Compression is needed for the combustion engine to run AND Exhaust!
6. Double ck the carb that all ports are open Good with wire or compressed carb cleaner.
7. That old, could it have a swollen rubber seat in the carb causing it to starve for fuel?
8. Will a prime restart it as soon as you give more fuel? Again, try to Detect Fire/Fuel/Compression.

    Bookmark   March 10, 2014 at 9:16PM
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rboone7760

The engine will run really good for 2 or 3 minutes, I did not time. The compression is very high, can only pull through one firing cycle when starting, the same after hot, no compression release. I tried to make the mixture richer with the low speed adjustment when the saw started running poorly but It did not help. After the engine dies you can restart it but it runs poorly. How do I check #6? Do I remove the adjustment screws and squirt carb cleaner?
This saw was given to me by my great uncle.

    Bookmark   March 10, 2014 at 10:47PM
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loger_gw

1. Depending on what you did in the carb rebuild, I would suggest the following to verify all ports are open.
2. I would suggest disassembling the carb, rem all rubber non metal Etc and soaking the carb 8 hrs in carb cleaner (with mixture screws removed).
3. Run wire, compressed carb cleaner or compressed air in all ports to verify they are opened.
4. If the saw sat with fuel in it years and untreated, it could be some stubborn varnish or debris in the carb.

    Bookmark   March 10, 2014 at 11:22PM
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