| Basic Carburetor Jetting By ScribnerAir/Fuel Mixture If you are having idling issues or poor
throttle response, the first thing to check is your air/fuel mixture. The
air/fuel mixture controls from idle to 1/4 throttle. The best way I have
found to check it is to let the bike warm up to operating temperature. Let
the bike idle in neutral and give it wide open throttle. If the bike has a
hesitation your mixture is off. If the bike bogs down and then revs up
fast it will be lean. An up and down or "rolling" idle is another symptom
of a lean mixture. If the bike idles rough and kind of low, it will be
rich. The best place to start with your settings is about 2 turns out.
Tighten the screw lightly until it seats and then back out and count
slowly. Pilot Jet If you get more than 3 full turns out on
your air/fuel mixture, you will need to step up on your pilot jet size. If
you get under 1 full turn then you will need to step down one size on your
pilot jet. Next Is Your Needle Your needle will control 1/4 through 3/4
throttle positions. If your bike is "popping" or "missing" at a constant
speed, your needle will need to be adjusted. If you give your bike full
throttle from a constant speed and experience a hesitation, you are lean
on your needle. You will need to lower the clip on the needle (this raises
the needle), allowing for more fuel flow through your needle tube (dump
tube). If the bike is trying to "load up" at a constant throttle position,
your needle setting is to rich. Raise the clip on your needle (this lowers
the needle), which will restrict the amount of fuel coming through your
needle tube. Needle Tube Your main jet screws into a brass tube in
your carburetor called the needle tube (dump tube). If you run out of
adjustment on your needle then you will need to replace it, although very
few times have I seen that this needed to be replaced. The only time that
I have seen it need to be replaced is when running methanol. Main Jet Your main jet controls 3/4 to full throttle.
If you are at wide open throttle and the bike is revving up but not really
pulling, you will be lean. If the bike is slow to rev, then you are rich.
The best way to check your main jet settings is to do a spark plug
reading. Run the bike at full throttle until top speed is reached, then
shut it off using the kill switch. Keep the throttle wide open until you
come to a full stop. Pull the plug and look at the porcelain down in the
plug. The all around best color is a light chocolate color on the plug. If
you run the bike at full throttle all the time you might want to run one
step bigger on the main jet, to keep the motor from burning up. If you run
short distances at full throttle (ie. racing) you can run one step smaller
on the main jet for maximum power, but keep the full throttle distances
short. | 
