Plug chop

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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 your 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 3rd, but it depends how fast your bike goes in each gear and where you're doing this test (trying to run a bike out in 4th is not advisable in, say, a school zone). At least get into 2nd gear.

2. Hold it there ... even though you will be nervous, hold it in gear at maximum 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 your normal use will be well within safe margins. Keep your hand on the clutch, as you could (doubt it, though) seize if you are jetted too lean to begin with. As always, use your own judgment!

3. Kill it. Simultaneously hit the kill switch and pull in the clutch. Hitting the kill stops the plug sparking and pulling the clutch stops the clutch from turning the engine over (bringing in more unburned 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 hot!!!

5. Read the plug. If the plug is:

Black and wet: your jetting is too rich.

Chocolate brown: your jetting is right on! you kick ass!

White and burnt smelling: your jetting is too lean! Upjet now . You might also notice a blistered insulator. This is real bad. You are lucky you haven't hurt your 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.

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Taken blatantly from Incriminator Sean's tech pages

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