[Shop-talk] Engine Vibration

[Bob Nogueira]

Ibve got a single cylinder motorcycle engine that was recently rebuilt,
Ibve got it running wonderfully except for a problem with a mid throttle
vibration.
At the upper end and at idle the vibration is not present to any great extent
but comes on very strong only at mid throttle with no load.

I was assured by the rebuilder that everything was okay. No major parts needed
to be replaced ( same piston, rod and crank).

Any suggestions as to where to look for a cause of the vibration?

Thanks
Bob