The Idle Mixture Screw adjustment is one of the single most important things that MUST BE CORRECT or your scooter will die at stop lights and stumble when you take off from a stop. The Idle mixture adjustment affects the IDLE ONLY! It has no effect on the high speed mixture whatsoever contrary to internet rumors. What it does is put the engine in a healthy idle so that when you open the throttle it doesn't stumble or stutter. It takes off like it should.
To set your idle:
1) Turn mixture screw on the side of the carburetor all the way in and then back it out 2 1/2 turns.
2) Warm up the scooter for at least 5 minutes, longer if you are in arctic weather.
3) With the scooter warmed and idling slowly (900-1200 rpm) on the center stand, turn the idle mixture screw SLOWLY to the right until the idle gets rough and slows even more.
4) At that point stop and turn screw back to the left SLOWLY until the idle smooths out and reaches it's maximum speed.
5) After you find the sweet spot, re-adjust the idle speed screw if needed to a speed just before the back wheel begins to spin with the wheel off the ground. If it spins you will fry the clutch at stop lights.
6) It may require some fiddling until you get it just right. You'll see.
The mixture is affected by seasonal temperature changes so it should be done 2 or 3 times a year as the weather changes, and after every valve adjustment.
Keeping the air filter clean on a regular basis will ensure proper idle mixture as well as high speed mixture.
Mixture screw:
Idle speed screw:
