Hi, this is actually a question for my dads motorbike which is a 1992 kawasaki gpx 250cc. When started it revs to about 4,000 then slowly comes down and depending where the throttle stop is stalls, as soon as its revved again it hovers around 4,000 and slowly drops back down to 1,000 or stalls. We have set the mixture screw to 1 and a half turns out but have tried 1, 2 and 2 and a quarter turns out. the carby's have been pulled apart and all the jets cleaned. The diaphrams are good and slide properly forgot to ask him about the air cleaner but if it didnt have 1 or have a good one could this be the problem? the spark plugs and spark has been tested by having the spark plug earthed against the cylinder head and the engine turned over and its a consistent blue spark. as far as I know the vacum lines are hooked up correctly but as the carby's have been off this is a potential contributer to the problem. once running it runs fine but could be lacking a bit of torque IMO though this could be the mixture screws not set right. Please offer suggestions of things to check/ do Thankyou!