the plug chop is an essential step in setting up jetting. not only does it help you get good performance, but more importantly, it helps you make sure yr bike is not running so lean that it will blow up!
1. wind it out! . warm the bike up well (5-10 min) with a new or fairly clean plug, correctly gapped, then wind the bike out in a gear. generally, i like to do this in 3d, but it depends how fast yr bike goes in each gear and where y’r doing this test (trying to run a bike out in 4th is not advisable in, say, a school zone). at least get into 2d.
2. hold it there … even though you will be nervous, hold it in gear at max rpm for a while… what you are trying to do here is simulate the hardest use the bike will ever conceivably see. if you jet for the most stressful conditions, then yr normal use will be well within safe margins. keep yr hand on the clutch, as you could (doubt it, though) seize if you are jetted too lean to begin with. as always, use yr own judgment!
3. kill it. simultaneously hit the kill switch and pull in the clutch. hitting the kill stops the plug sparking; pulling the clutch stops the clutch from turning the engine over (bringing in more unburnt fuel). thus, you get a perfect picture of what the sparkplug looks like at the moment you hit the kill switch.
4. pull over, pull the plug out you will want to have gloves or a set of pliers, cause the plug will be fking hot!!!
5. read the plug. if the plug is:
black and wet: yr jetting is too rich
chocolate brown: yr jetting is right on! you kick ass!
white and burnt smelling: yr jetting is too lean! upjet now . you might also notice a blistered insulator. this is real bad. you are lucky you haven’t hurt yr bike worse!
6. important note: heat grade of the plug will also affect the color the plug reads… if you use a ‘cold’ plug like an ngk b9, you will be more likely to get a richer plug reading. however, in my experience, plug grade –as long as you are within the normal spread of plugs, f.x. malossi 210s take between b7es and b9es — is not terribly important when doing initial jetting setup. for finer tuning, plug choice does make a difference, however.