When rejetting my Vinson, do I go higher on the number for rich or lean?
It has a Keihin carb. It is popping when i let off the gas, and backfires
after a long, hard high speed run. I am assuming it is running lean
in the bottom end or midrange. Adjusting the pilot screw did not help.
Also, moving the clip up or down is rich or lean? Clip up for lean or rich?

 

The larger the number the more fuel it'll let in (richer). Do you have a jet kit, cause the stock needle doesn't have no clip adjustment. Anyway by moving the clip up will lean it out in the midrange. The backfirering should just be the idle mixture screw on the bottom, turn it out 1/4 at a time and test.