Aack!!! I am hopeing someone has some ideas out there. My motor has nast vibration at about 2000-2500 rpms, then it smooths out. Idles fine, then vibrates, then smooth. It vibrates with or without the clutch engaged. Any ideas?
might be a crazy place to start, but will it vibrate sitting in the driveway as you increase throttle to test? If so, get someone to rev it up, (or do it yourself at the carb) and see if either of the water pumb/fan pulleys are eccentric/missaligned etc..
i.e look at anything on the engine you can see from the outside that spins/rotates and start eliminating the easy stuff.