You can not go by what the spark plug looks like. You have to do plug chops. This involves warming the engine up, installing a new plug, and starting it, then immediately running it wide open for a mile or two. When you're done, kill the ignition while keeping the throttle wide open. Let the engine come to a complete stop before letting go of the throttle. Pull the plug and look at the white insulator inside. You want a coffee(cream coffee) color on that insulator. There will be a ring of coloration. The distance from the tip also indicates fuel air mix. You can cut the threads off to get a better look(hence the name "plug chop") Here is a good link
http://www.kawtriple.com/mraxl/carb/plugchop.htm
This is from page one of this thread
At this point you may need to do a compression test. Running lean will ruin things quick. You want at least 120 psi. That's the bare minimum though. You should have around 140 or more.
Plug chop step by step:
1. Buy several new spark plugs
2. Warm the engine up with the old plug
3. Find a stretch of road you can run the scooter wide open on maybe 2 or 3 miles. You need a good starting place and a good stopping place(you'll find out why in a minute). I'll pull into somebody's driveway if I have to.
4. Install a new plug at the starting place(careful the old plug you take out will be hot). Be close to the road because you want to go full throttle within a few seconds of starting the engine
5. Be ready to go(no traffic coming). Start the engine and take off right away.
Full throttle. It's very important you maintain full throttle through the whole run.
6. This next step is equally as important. As you approach your stopping place(last 100 ft or so), Keep the throttle wide open and kill the engine will the red kill switch on the handle bar. I repeat, hit the kill switch while still holding the throttle wide open. Slow down and let the engine come to a
complete stop before you let go of the throttle.
7. Remove the test plug and reinstall the old one(caution hot)
8. Drive home and take a look at the results. I suggest cutting the threads off the plug to get a good look at the smoke ring. Take a look at this link again. It will give you a good idea of what the ring should look like.
http://www.kawtriple.com/mraxl/carb/plugchop.htmThis is for checking if the main jet is lean or rich. You can use this same method to check mid range(needle setting) as well as idle. Mid range, you would just hold the throttle halfway during the test. Idle is easy.
