I have a 1994 Phazer II with pull start that has a rhythmic clunking sound when under load going up a grade. (It might be present going downhill, but if it is it's too quiet to be audible.) It is definitely drive train related, as it only happens when moving, and speeds up or slows down with sled speed, not motor RPMs. I have checked and adjusted both sheaves, the secondary sheave alignment and free play, the drive chain tension and the track tension. I have also checked motor mounts and all of the track guides and wheels for alignment, tightness and play. The biggest problem in diagnosis is when I lay it on it's side and run the track, it doesn't make the noise because it is not pulling a grade with a load.
This is making me crazy. Does anyone have any ideas?