I have a 97 Suzuki RF 900 R that I´ve had for about 2 years. I am a retired engineer and have modified it into a sport bike with an upright riding position similar to the Honda 700 CTX. It runs great except for one problem. Unless the idle screw is all the way down so that it will hardly idle, the bike tends to want to run on and is slow to get back to idle after the throttle is open. The local mechanic said it might be an air leak between the carburetors and the intake ports. But there is no leak, it is all very tight. Does anyone have an idea on what to check next?