1. Get new spark plug(s), but don't put them in yet.
2. Warm up motor to operating temp on old plugs.
3. Install new plugs.
4. Accellerate through all gears to top gear with throttle pinned.
5. When you hit the top of the top gear, hit the kill switch and
pull in the clutch.
6. Remove the spark plug(s) and ride home on the old plug(s).
7. Hold the new plug in a vise and use a hacksaw to cut the threads
away from the center electrode.
8. You should see a brown 2mm "smoke ring" at the base of the
white center electrode if the main jets are dialed in perfect.
9. if the smoke ring is darker than chocolate brown or taller
than 2mm, you're rich on the mains, but if it revs clean to full
throttle, you can leave it there and be on the rich side.
10. If the smoke ring is smaller than 2mm or lighter than chocolate
brown, you're lean on the mains, go up a size and try again.
Chopped plug Illustration:
