As I mentioned in this thread, my old FS86 was slowly loosing power and becoming more temperamental: http://www.arboristsite.com/communi...112-1-with-a-wt-45a-on-a-fs86-trimmer.310522/ Compression was OK at ~140psi and the spark was solid, so I decided that it must be a fuel problem, so I replaced the carburetor with the hope it would address the issue. With the new carburetor the trimmer would start and run but had little power and wouldn't rev up beyond 8,000 rpm and got their slowly. As soon as you started cutting with it, the motor would bog down and quit if you didn't give it time to spin back up. Still thinking this was a fuel problem, I removed the fuel filter in the tank thinking that the if it was clogged it could starve the engine for fuel, or collapse the fuel line and cause the same result. Started it up again and it was still dogging. Now convinced that the issue was outside of the fuel delivery system and carburetor, had to look elsewhere. Next thought was a vacuum leak. Oh how I was hoping that I didn't need to replace the crankshaft seals. Trying to avoid that need, I removed the cylinder shield and put a T27 driver on the cylinder bolts. Oh my! Got a close to a full turn on the first one, and almost as much on the second. The two on the clutch side of the cylinder pretty tight and only took a 1/4 turn or so. Put the cover back in place and hooked up the throttle cable and a couple of pulls on the starting cord and the saw came to life. With carburetor adjustments the engine was running at 10,000 rpm and powered through the tall ditch grass that was needing to be cut. Let set overnight, and just tried to start it. Two pulls with the choke on, and one pull with the choke off and it was off and running.