A large number of emails I get in my DON'T ASK column deal with jetting. More specifically, bad jetting. The two main reasons for crappy jetting are:

1. Most bikes (up until a few years ago) came jetted too rich from the factory. Riders assumed this was normal and, blissfully ignorant, just went ahead rode the bike the way it was, changing plugs when they fouled, assuming that was normal.
2. People modify bikes by swapping pipes, reeds, carbs or whatever and have no

   clue on how to re-jet the bike properly after the change is done.

In order to make things clear as to what's happening in your engine, all you have to do is remove your spark plug and compare it to the color photos show here.

However, here are some things you should know before you start swapping jets:

• Let's say your plug reads all sooty and black, which is a sure sign of running too rich. So you lean out your jetting. Give the bike a run and take another look at the plug. Wrong! Before you take that run, you should put in a FRESH PLUG. That's right. If you just take a hot run and then yank the plug to see what's up, it'll still have the old crud on it. The only way to get a clean reading is with a new plug. Don't complain. They're only a buck or so each.
• When you run the bike for a plug check, make the engine work hard. An ideal situation would be a slightly uphill sandwash at full throttle in whatever gear the bike will pull at full throttle.
• As soon as you complete the run, quickly go back to the pits/parking area and chop the throttle and the kill button as soon as you can, letting the bike coast to a stop with no power.
• Then yank the plug and take the fresh reading. If it reads properly and there's no sign of pinging or detonation, you're got it right.

Now here's a guideline:

NORMAL CONDITION
If the inner tip is dark-brown-to-light-tan color with slight deposits and slight electrode wear, with a slightly darker outer ring, you're in the ballpark.

RICH CONDITION
When your plug appears sooty black, with heavy carbon deposits, you are overly rich on the jetting. What can cause this? Rich air-fuel mixture, dirty air filter, excessive low speed operation, weak ignition or incorrect heat range.

FOULED PLUG
You've got a slimy plug with wet, black and oily deposits. Not a good sign. Possible causes: Excessive low speed operation, using an oil that is not recommended and/or an incorrect premix ratio, low compression, weak ignition, incorrect heat range and/or spark gap or excessive exhaust carbon buildup, worn top end parts, leaking mag seal or badly clogged air filter.

OVERHEATING/TOO LEAN CONDITION
The tip and/or outer ring is light gray or white in color. Insulator nose blistered, glazed, cracked or shows signs of aluminum speckles, and the electrodes are burned. May be accompanied by an audible pinging/rattling sound, also known as a death rattle.
Possible causes include: Lean air-fuel mixture or air leak, incorrect timing, insufficient cooling, incorrect spark plug, heat range or improper spark plug insulation.

DEPOSITS ON PLUG
Sometimes you'll yank a plug out ad it looks like it was dropped in the dirt with bits of crud stuck on. There could be carbon deposits lodged between the side and center electrode. The possible causes are: Excessive amount of carbon buildup, using an oil that is not recommended and/or an incorrect premix ratio, or dirt bypassing the air filter.