small vibration

[ub6ib9]

hey, i have an issue with my spare SN 650, i let a larger (260ish) friend give it a shot trying to ride for the first time last summer, it hadnt been out in a long time, definitely was in need of a tune up so she wasnt running that great, he tried to get out of the water a few times but just couldn't lol, i heard it backfire and bog out and after falling off again he gave up.

fast forward a few days later after i had it tuned up and went for a rip, there was a definite vibration there that wasn't the last time i rode it. its most definitely noticeable but i cant figure out what it could be.

Is there any way he couldve twisted the crank when it backfired while trying to lift him out of the water? or is it possible the midshaft could have been slightly bent?

im gonna bring it out of storage next week and look into it a bit but i wanted to see what you all think. is it possible to even diagnose a very minor imperfection in the crank without tearing it down? or how i can check the midshaft to see if its off center.

i do know forsure its not the coupler though

 

[john zigler]

Yamaha cranks are very tough, I highly doubt you are out of phase. You could check, one cyl would be dead on bottom dead center, and the other should be dead on top dead center. Use Dial indicators to check.

Same with mid shaft, it is so short, there is no way he could have "bent" it.

I am betting something came loose, or you have an old rotted, bad engine mount. Look also at your drive line. Common issues are bearings in the mid shaft assembly, and pump.