Originally posted by Brett.w
i kind of had the same problem yesterday, for no reason all the botom end went, i changed the plug, checked the clutch and did the pinch test every thing seemed ok so i am kinda stumped! but when it did pick up it was real good.
I guys
Airleaking.........that's the problem. So far i had same problem in 1 engine. The 2 cams that you use to fix the carb at the crankcase in some case are some tents too long, and so even if you tigth the screw all the way down, still the carb is not really tigth and some air leaks from there (i had 1 engine that with the screw all the way, the carb was loose :weird
To solve this, you need to take out the 2 cams, grind a little bit and then the problem is solved.
Anyway, if there is no airleaking and the engine is running good and progressively is becoming lean, i normally rich the HSN (wich since is the "main" needle, it will also rich the bottom at the same time.
About compression, at sea level with 16% you should use 0.3 mm. Anyway, reading the plug is the best way for me
Another tip is the oring inside the crankcase (there is an internal oring inside the crank where the carb is located. I have had some bad experience with the internal oring cause the fit is so tigth that in several cases when you install the carb you strip the oring and the black parts goes in the crankshaft making a mess (not a big problem, is easy to solve, but anyway). I am using my engines without the oring (i use only the oring that is in the carb and no problem at all.
Paolo