Did you check out the clutch carrier in the driven clutch? If worn down,it can cause harsh engagement also. 75 bucks for an oem or you can get an aftermarket one on ebay for 29 bucks if needed.

 

Yes, I looked at the part you show above. It looked almost new but the outside edges had some grooves like from dirt or who knows what rubbing when not enguaged. Also the inside of the housing had slight grooves. What throws me off is when it does engage it does it hard and it takes off, not like a slipping clutch on a car or cycle when it slips then catches up to rpm after enguaged.

 

Then if you can rule out clutches or the belt,it could be a shift fork or engagement dog problem that abruptly locks in when you give it throttle. The early Phoenix and Sawtooth were kinda like that. People when shifting into gear,if they didn't hear a positive "clunk" going into gear,they could barely give them throttle and most then would clunk into gear. After that they could give it full throttle with no problems.This was more of a design problem as almost all of them did this.On the little 90 this could very well be an engagement problem like these machines or could be a worn shift drum,shift fork or slider gear.
Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse

 

That sounds more like my symptoms and possible cause.
If I brake hard I can give it 3/4 throttle until I hear a clunk then let off and start out slow. If I don't brake it takes off at the clunk at 3/4 throttle like a stall on a drag car launching pretty hard.
if it does turn out to be a worn shift drum, shift fork or slider gear, will anything else get wrecked driving it as is and just keep using the brakes for initial engagement?
I really don't have another $100-300 to throw at it at the moment if it already needs replacing and wont hurt any of the other parts in the process.


Thanks for the help

 

Shouldn't hurt anymore than it already has..