Good Evening~
My husband recently purchased a 1985 LT250R from our neighbor. One day while riding it, it began to idle extremely high, so he immediately shut it off and brought it home. We thought it was an issue with the carb, and so we had it rebuilt by one of our local shops. He reinstalled the carb and reassembled the quad last night, but now as soon as he starts it, it is idling so high it sounds like it's going to blow! He has tried to make adjustments to the carb with no luck. Any suggestions would be greatly appreciated!

 

Problem Solved!!

Cause of idle issue: Seal Leaking

Solution: He took the carb off, plugged the intake and the exhaust. He put plastic over the opening and collared them down. Then with the spark plug out and the piston in the bottom position, he stuck a rubber nosed air nozzle into the spark plug hole and pressurized the chamber and heard where the air was leaking. It was clearly leaking behind the magneto- the main seal was pushed out. He replaced the main seal, and now all is good. Happy riding!!

 

my 1987 lt250r does that too. It scared me at first but I learned to live with it. Whenever it starts reving up I hold the break and engage first gear and the reving goes back down to a normal idle. don't know why but it hasn't stopped me from riding.

 

Welcome to the forums.
You need to fix that seal before it leans the quad out and sticks a piston.