Thread: Chainsaw question - engine dies

Originally Posted by hotbarrels

Is the compression test the same as a 4 stroke?
Vacuum testing?

Compression is the same as four stroke, reading the max cylinder pressure that the cylinder and piston can produce. Vaccum testing is a little different, usually you blank plate the air filter end of the carb and the exhaust port and with the piston at the bottom of its stroke pull a slight vacuum with a hand pump tester (screwed into the spark plug hole for the one I have access too). This checks basically everything soft that seals the crank case, crankshaft seals and any gaskets and rubber boots to make sure that there isn't any air leaks into the crank case leaning the engine out.

Well, thats the theory I have on it - there are other tests that people do that a supposed to show leaks but some of it seems like black magic and snake oil to me to be honest...

And that compression test I did on that little generator - that was after about three odd weeks on and off including waiting for bits ordered from China so not really my finest work. Seems that as far as I can figure someone had been into it a little before me and rewired it wrong which meant no spark (despite the owner telling me he hadn't done anything with it and just packed it away).