I had a friend ask me about a high idle problem she was having once her 2007 Suzuki GSX-R600 was warm after a long ride. She said the r.p.m.’s would climb to nearly 2,000, then drop down once the motor cooled off. I’m familiar with this problem, as the 2005 Suzuki GSX-R1000 I’ve been riding was having a rough, low idle problem and would stall when cold. I corrected the idle, increasing the idle r.p.m.’s with the idle adjustment screw from 1,200 r.p.m’s to 1,500 r.p.m.’s, but the bike would still stall when cold then rev high when warm.
I then checked the valve clearances to the camshafts with a feeler gauge to make sure they weren’t too tight, as tight clearance from the tip of the valve stems to the cam shafts in the top end of the motor can cause stalling issues on higher mileage bikes. The clearances were all within factory specification, so I started up the bike and played with the fast idle screw, which is the smaller screw just underneath the idle adjustment screw on the throttle body. This screw controls the clearance between the arm (holding the throttle cables) and the larger idle adjustment screw.
There I found if I adjusted the fast idle screw too far up toward the arm thus creating a tight clearance between the two, it solved my rough idle issue but the r.p.m.’s would be too high once the bike was warm. Now that I knew I compensated too much, I adjusted the fast idle screw out so as to have a little bit of slack between the screw and the arm. With the bike running, I then rotated the larger idle adjustment in (toward the air box) and was able to solve both the rough idle problem and the high idle problem when the bike was warm. It was just a matter of getting the fast idle screw adjusted correctly before rotating the larger idle adjustment screw in or out.
The factory does not recommend messing with the fast idle screw, but if you are having a high idle problem, this can act as a band aid until you’re able to synch the throttle bodies during the next service. All you need is a 4mm or 5mm T-allen to remove the seat and gas tank and a phillips head screw driver (with a small butt handle, no bigger than your pinky finger) to adjust the screws. When you adjust the fast idle screw, you want just a little bit of slack between the screw and the arm. I learned this from the Kawasaki Team Green mechanics as they used to adjust the same type of screw inside the carburetor to sharpen throttle response on the KX250’s.
This is by far not a precise or factory recommended explanation, but it has worked for me.