I need a little help here. I just bought a '94 160 cc Quadrunner and I really don't know anything about these. It stalls when it goes to idle. I can't turn the idle screw in any farther so I'm thinking it's the air screw. Can anyone tell me which screw is the air screw? Are there any other adjustments for idle? Also, there is a kind of plunger under the tank that you can pull in and out about a quarter of an inch. Can anyone tell me what that is? Any help would be appreciated.