Idle problem

[super90]

Me and my friend are trying to figure out how to fix his carb, it will idle good but when you give it gas it revs up fine but then hesitates to drop back down to normal idle rpm's. We lowered the needle clip all the way down and that made the difference between dying and idling. Played with the mixture screw and airbox on/off. Im just curious how to fix this since my engine did the same thing and I never figured out how to fix it. Thanks

[atc500x]

When your engine is idling,play with the air screw.Note if the is a difference on idling when you screw it completly.Maybe need to adjust fuel level,dirty carb
Check the intake for crack in rubber.Ignition timming

[super90]

There is a difference. When you screw it in all the way and lean it out it idles very high. When you screw it out a few turns it idle but stays revved up longer. Finally when its out another 1/2 turn it floods out and will not idle. The carb was just rebuilt and fully cleaned. There are no cracks in the intake boot or anything. I see how an air leak could cause this but Im almost positive this isnt the case. Im guessing the carb just needs tuned up, but I never had this problem before and dont know how to solve it.

[Erics350x]

First clean the slow jet real good and run a small peice of wire through it to clear any stuck in crud.

There should be a rubber o-ring on the mixture screw. If the o-ring is missing it'll never adjust right.
Another thing to look at is valve adjustment. < assuming its a 4-stroke

What engine are we talking about?

[super90]

The engine is a 1987 200x engine. The valves have never been adjusted in it before while he has owned it I know. The carb has been throughly cleaned with everything completely taken apart and soaked, scraped through and blown out.