Chainsaw has fuel, spark and compression but wont start

Question

A neighbor gave me a chainsaw to fix. He does lawn care and landscaping so I'm assuming it was used a decent amount. I think it just sat through the winter and then wouldn't start.
I gave 5-10 yanks, and it fired right up. Shut it off, tried to start it again and it started and died. Now I don't get anything. Pretty sure it's getting gas, the plug comes out wet and sometimes after pulling for a while some will dump out of the cylinder when I turn it upside down. It has spark, maybe a little weak, not sure, so that's my main guess, but no idea what is causing it. Everything looks OK. Pretty sure its not compression because it did start that one time, and I took off the muffler and didn't see any scoring.
Any ideas or advice? Thanks!

mongo · Accepted Answer

In your situation, the most common cause is gasoline which has deteriorated and is blocking lines, pump, carburetor or other parts of the fuel system.  Just having a wet spark plug does not assure proper mixing and atomization of the fuel.
The normal fix is to drain the fuel system, replace the fuel, and "rebuild" the carburetor, which is a cleaning and replacement of diaphrams, valves, etc.
The next likely cause is possible loss of timing alignment.  If there was no trauma to the saw's motor, this is unlikely.  However if it happened, you could still get spark without combustion.

Chainsaw has fuel, spark and compression but wont start

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