I have two 87 lt 80 quads both are stock and both hate it when i go thru a lot of water they run fine but they wont move but very slowly at the very bottom of the rpm range they have done it a few times now and seem to be fine when they dry out although it sucks pushing them back home so if someone knows how to fix this problem I would like to know

 

Check your belt cover seal, even buy a new one if you must, it happens to a couple guys i know, it is because their case wasn't sealing properly.

 

there is a drain bolt at the bottom towards the back of the belt case. Or you could have a bad clutch or glazed belt but I would bet your getting water in there. Also I would lube up the clutch rollers if you have been riding them through water.