I have a Revtech 100, mikuni 42, any speed under load acceleration. there is a chatter as soon as slightly letting off throttle it stops...had idle a bit low and it seemed worse, brought the idle up just a bit and seemed better...Any Ideas or direction be appreciated...

 

Sounds like it may be piston slap.

 

May also be pre detonation (knock sensor / carbon build up / bad fuel / carb not jetted correctly..., jets gummed up / plugs too hot)

Try changing the oil and adding seafoam to the gas - run a tank or two thru to see if it improves


More detail would also be helpful - this chatter - just start..., or been this way for awhile

What was done to the motor just prior to it chattering



Ghost

 

... or bad gas, try adding an octane booster for starters

 

It's your ol' lady on the back telling you to slow down. Not sure what you mean by chatter but if you are talking about pinging I agree that octane booster is the first thing to try before you destroy your engine. If that helps then maybe a top end tear down is in order to diagnose the problem. What compression ratio are you running?

Dan