I have a Kymco mongoose 90. Long story, but it sat in a warehouse for 8 years. Almost brand new. Replaced the carb and it ran better, but it will only move if I give it full throttle and push it. If I lift the rear end, it runs fine. Does anyone have any experience with this? Any suggestions would be appreciated.

 

Sounds like you need to pull the clutch cover and clean/check out the belt and clutches.Sitting up 8 years,there could be corrosion on the clutches causing sticking or the belt could be cracked and need replacement also.

 

I've found mice to be the main culprit.

 

I just took the belt off. It looked good, but I wanted a second opinion, so I took it to the dealer. He thought it looked good. I took carb cleaner to the clutch. What should I look for on the clutches?

 

What did they do?

 

They make nests and their wastes cause problems.
With you having the belt off, this isn't your situation.
IMO you'll have to remove both front and rear clutch and inspect.
Front for bad rollers(doubtful) and make sure it slides on the spacer. Rear: squeeze the clutch face. It should slide. If all that is freely working, it's not the clutch.

 

Easiest way to know if clutches are working is to run it with rear wheels off the ground and clutch cover off...if clutch sheaves move with changes in RPM then all is good...if not...not so good...this is how us sledders validate full shift-out...