Has anyone experienced a situation where a motor conversion deal (motor adapted to some racing lower) had a drive shaft vibration (due to misalignment or ?). If so, was the bite of the prop affected, causing excessive slip?

I have a mystery problem where the same boat with the same prop and lower unit, but running a motor with a lot more power, makes 5 mph LESS speed at the same rpms. The more powerful motor weighs 30 pounds more, but other than that everything is the same.

Thanks for any input.


Jeff