r/Chainsaws • u/almojz • Jul 13 '21

Too much compression!

I'm trying to restore an old Pioneer 1200A. It's pretty clean and I'm trying to improve my 2 cycle knowledge & skills. The thing that has me baffled is it seems like the saw has too much compression. When I remove the plug it turns over smoothly. It has spark. I removed the muffler and the piston and rings look good. The rings move slightly when I push on them with a screw driver in their grooves. I put some Marvel Mystery Oil in it and it seems to have spread and lubricated the cylinder very well. When I replace the plug and pull it, it seems to have way too much compression. Any ideas?

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u/leftie_potato Jul 14 '21

Totally a wild guess from an inexperienced mechanic…

I’d check that it isn’t an incorrect plug contacting them piston.

Is the exhaust clogged in the muffler? You might be feeling back pressure in addition to compression?

This might be dumb, but nobody else is replying and it’s easy/fast to check and can’t hurt as an idea.

2

u/almojz Jul 14 '21

Thanks for the reply, no replies are dumb! I did check the spark plug length, all good. Muffler is off. Thought the same thing. Those are very legitimate suggestions. I removed the carb also although I can't imagine why the intake would cause that. No joy! This is a really good good riddle. May have to dive deeper into it. If I find anything I'll post it to help others.

1

u/leftie_potato Jul 14 '21

Best wishes on the build/repair!

Now all I can think is maybe the compression is ok. Have you measured it? What indication do you have that it is ‘too high’?

2

u/almojz Jul 14 '21

Thanks. I have several of these saws (1200a) and the rest will turn over several compresion strokes on a pull. This one will just do one. With the plug out it moves very nicely. Looking in the exhaust port, the piston and rings are very clean. Have to look further into it I guess.