My friend just got an 87 250r and there is something wrong with the low end(idle-1/4 throttle) The rest is perfect. It seems to bog at the low end. It doesn't respond until you hit 1/2 throttle. The carb is all stock and he has stock pipe&silencer. Is it the pilot jet or should he look elswhere like clogged silencer,reeds.
Messing with the air screw does nothing, but it seems too rich. THANKS

 

Yes it is the pilot jet if the problem is just off idle. It is most likely too big and should try stepping down one size.
The air screw; turn all the way in and then back out 1 7/8 turns. Start the engine and after it warms up, turn the screw in and then back out until it idles the fastest. Stop there.
Reeds, if you take them out, make sure they all sit flat against the cage. If they are warped, chipped, etc., they will need to be replaced. Bad reeds will also keep it from idleing properly.
Good luck!