What are standard settings for idle and air mixture screws
The idle speed will be dependent on model, particularly if 4- or 2-cycle, 2, 4, 6 cylinders, etc. If your engine uses carburetors, I'd say no less than 600 RPM, maybe up to 850 RPM at idle. If your engine is fuel injected, the computer should set the idle speed and air mixture for you (if it's functioning correctly), and a big twin could idle as high as 1150 RPM .
Your Idle air mixture settings are important for proper idle. A good approach is to let the engine tell you what it likes. For this method you will need either a tachometer or a vacuum gauge. Here are some steps to guide you.
1) If the engine will start and run, go from there. If not, a good initial setting is to turn the idle screw(s) all the way in (GENTLY--don't break the seats!), then back them out about 1 1/2 to 2 1/2 turns.
2) Attach either your tachometer or vacuum gauge to your engine. Tach is connected to the ignition system (usually at the coil); vacuum gauge would be connected to a manifold vacuum port. (The bike's built-in tach MAY work for this, but they are often not graduated finely enough.)
3) If using a tachometer, warm up the engine. Working on only one idle mixture screw at a time, begin turning it IN until RPM begins to decrease. Then back the screw OUT again until you achieve maximum RPM on that screw. Feel free to "play," turning the screw in and out until you achieve highest RPM at at minimum turn-out (if you leave it turned out too far, bike will run rich and foul spark plugs; if not far enough, bike will run lean and hot). Now do the other idle mixture screws the same way. Finally, go back and do all the mixture screws again (and again and again, if necessary) until all throttle bores are synchronized.
4) If using a vacuum gauge, engine temp is not as critical, but go ahead and warm it up anyway. Similarly to the tachometer method, turn the mixture screws in until RPM drops, then out until max vacuum reading at minimum turn-out. If you have multiple mixture screws, do the same on each, then repeat on all screws until you feel they are all synchronized.
5) Throughout the process of adjusting idle air mixture screws, you will probably have to adjust the idle screws to keep the engine in the RPM range you want it to idle. (If adjusting air mixture screws has no effect on the engine idle, the minimum requirement is probably a carburetor rebuild.)
6) Have fun getting to know what your engine "likes!"
Oct 14, 2014 |