Merry Christmas,
I bought a new engine off of Ebay for my kids coolster 125quad. The original engine ran great til I put royal purple synthetic in and it turned to molasses. I think I burned up the clutch. Anyway, I put this new engine in without a problem but it has MAD, CRAZY vibration between rev and idle on the downward slope of the RPM. It smokes quite a bit when the throttle is stabbed too and will occasionally stall. Does this sound familiar to any one?