- Joined
- Feb 17, 2009
- Messages
- 16,682
- Reaction score
- 15,905
- Location
- Beautiful Rockbound Coast of Maine
While you're at it, for the price, replace the decomp. I just replaced the top end on a Stihl 660 that had similar damage to the piston. The saw wouldn't stay running. After tearing into it, I found that the decomp was shot. It had zero "pop" to its movement. I suspect that the bad decomp was leaking which not only killed compression but the leaked air was leaning out the mixture and created a hot spot on the piston.
Good advise...….except the 621 never came with a decomp...…..the only true Jonsereds that ever came with a decomp was the 87cc Jonsereds 90, the 87cc Jonsereds 910E/EV and the Jonsereds 111S.