2 cycle compression ......
 

On Mar 26, 7:45*pm, "Steve B" wrote:
I have a 21cc hedge trimmer. *A Craftsman. *It hasn't run for a while, but
the guy swore it was running when put up.

I put new gas in it, and checked the obvious. *It needed a new on/off
switch. *It has spark. *I can't get it to pop, even with shooting a little
gas into the carb, or on the sponge air cleaner.

When I pull the start rope, there isn't very much "POP" at all. *I mean
resistance that would come from good compression, or from firing and
igniting the gas/air mixture.

Just how much "POP" should be present, even if you have the switch off, and
aren't trying to start it, but just basically see how much compression it
has? *I call "POP" that instantaneous resistance on the pull rope where it
would hit TDC, or fire with a spark. *Does two strokes not have the "POP"
that four strokes have because of their different configuration?

Tomorrow, I'll pull the carb and see if there's anything obvious there. *The
primer bulb worked, no leakage, and filled up, presumably feeding gas to the
carb.

Steve

A weak spark may not spark at all under compression and fuel load,I've
had that happen on ignition modules or coils nearing failure. Even a
bad plug can do that. Is spark weak. For 10-15$ get a compression
tester, if you have other old motors it will get good use, don't guess
on compression, the exact pounds show how much engine life is left,
weak compression weak spark could make it not fire.