I've noticed that as long as I have owned my '86 Bayou, it hasn't held me back when going downhill like it should. My brother has a 250 Bayou with no brakes at all, and he han creep downhill as slowly as I can with me laying right on the brakes. It slows me down quite a bit, but the rpms don't seem to ever really come down like my brother's does when he's using the engine to hold him back.
I noticed that after I adjusted the carburetor out 2 turns according to the repair manual I just bought, it made the problem much worse. I've been turning the screw back in a bit at a time and it's as good as it's ever been with the screw out about 1 turn so I'm guessing it might be carburetor related. I'd like to have it working properly and not have to be hard on the brakes on every hill I go down.
It has a brand new top end on with about 20 hours on it so low compression shouldn't be the problem. Any ideas?

 

You have two idle screws, one is for the air/fuel mixture when idling and the other a throttle stop, which stops the throttle from quite closing, which would result in the engine stalling. It looks like you have been adjusting the mixture screw, this is factory set and doesn't need altering, unless your engine has been heavily modified. The throttle stop screw alters how fast the bike idles, set it just fast enough not to stall at idle.

 

I keep the throttle stop screw set so low that it barely idles. As far as the mixture screw, I had never touched it until I got the manual and read that it was supposed to be out 2-1/8 turns so I figured I would check it out since it doesn't seem to accelerate overly fast compared to my brother's 250. With it out 2 turns, no matter how low I set the idle, I had no engine braking at all and it would rev so high that I would have to hit the kill switch to get it idled back down. It seems to work best with the screw out only 1 turn. I have another carburetor housing I might try.

 

In a automatic its the 1 way bearing in the drive train that makes the wheelers slow, ie engine braking.
Not too sure about the bayou, but if its a manual then the engine will be pushed to a certain point just by gravity. Is it a manual? and are you downshifting if it is?

 

It's manual and I am downshifting. My brother can put his bike in first or second gear and idle down hills as slowly as he wants to. If I did the same, mine would rev so high that it would ruin the motor.