Chainsaw Repair

decompression button pops ,closes ,when pulling starter
it does not fire up or start
what could be the problem?
it pulls very hard when the compression is closed

Pull muffler and look at front of piston and back of cylinder for scoring aka scuffs.  Pull plug look at front of cylinder with flashlight through hole. Look for scuffing.

Check for spark to plug.

NOTE--It helps to follow the starting procedure recommended by Stihl.   I rearely deal with Stihl saws,  esp. newer ones,  so it was a learning experience for me.  Sometimes I'm a bit dense .

I had a MS 361 that i got from a pawn shop,  it started & ran at the PS.   I got it home,  dumped the old fuel,  gave it a good inspection,  reinstalled everything,  & fueled with my mix.   It started & ran fine;  I gently revved for a while (no wood to test it ) to let the fresh fuel work it's way through the carb.

A few days later it wouldn't start at all.   I ended up having to 'reconnect' the spark plug wire to the spark plug cap.   I'm thinking that someone pulled & yanked on it when it first wouldn't break free,  a mistake that I've made working on my cars.

working on the spark plug
seems the spark is not at the electrode
the spark is in
 other places like blue flashes
have the lights out to see it better
new module with new wires installed
short somewhere? flyweel ?
holding the plug to the cylinder head
to check the spark

Maybe a new spark plug would hep? My 361 was hard to start early on, opening the L side up a little made a huge improvement, especially when warm. I have also heard of the decomp valves popping on a high compression saw even if it didn't start. Never had it happen myself, but possible I suppose.