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The easiest thing to do is a "plug chop". This involves running the bike flat out in top (6th) gear, near the "red-line", i.e., 12000rpm, for at least 10 seconds, preferably slightly uphill so the motor is under slightly more load. Two things to note here, firstly, that if the bike won't pull cleanly to 12000rpm, there is something inherently wrong with the MJ or needle set-up, and secondly, to accurately gauge a "plug-chop" you need fresh, clean plugs! Also, allowing the engine to run off of full throttle for only a second will give a false plug reading.
NOTE: It is harder to "read" a plug if Super Unleaded (i.e. higher octane) fuel is used over leaded fuel, as it burns more fiercely and therefore more cleanly. For more information on this see the Fuel section earlier on this page.
So, at the end of a long enough straight to run flat out for 10 seconds, pull the clutch in, flick the kill switch, and coast to a halt. Remove the spark plugs, and check the colour of their respective electrodes, noting which cylinder each plug came from. They should be a light tan colour if your settings are good. Too dark, or black, and it's rich, if the plugs are grey you are too lean, and if they are near white, you are dangerously lean!!
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