Questions:

1. What does and doesn't plug reading tell you?

2. Does it only tell you if your main jet is too big or too small? The proper procedure for this is too bring your ATV up to operating temperature and then while riding it, open up the throttle full, pullin the clutch & cut the ignition? Does it matter if you cut the ignition before you reach max RPM, as long as you open the throttle full for a second?

3. Can it be used to determine if your jet needle is too lean or rich? If so, what is the correct procedure? Same as for main jet, except cut ignition at half throttle opening? Can this one be done while in neutral, or does the motor need to be under load?

4. Can it be used to determine if your pilot jet is too lean or rich? If, so what is the proper procedure? Ride in first or second at less than 1/4 throttle? Can this one be done simply by coming to a stop and letting the ATV idle for a minute?

5. Will your plug reading be different when the engine is just starting to warm up as opposed to when it has been at full operating temperature for a while?

6. What do hot and cold plugs do for you? When should you consider making a temperature rating change?

7. Can there be differences in plug readings between "equivalent" standard sparks plugs from different companies such as NGK vs. Champion?

8. Does an 8 temperature rating for an NGK plug equal an 8 temperature rating for a Champion plug?

9. What can go wrong and give you a false spark plug reading?

10. If you take a "random" reading of your plug by removing it at any given time without following any procedure, should it ever be near white?

11. Is this good information - www.centuryperformance.com/spark.htm?

 

Scooby, a plug reading reveals the richness of the fuel-air mixture. Regarding your question # 2, you MUST operate the engine for a time in the rpm range of interest before you hit the kill switch; think of the plug as a camera's film; you must expose the film toward the subject of interest if you want to capture the image. If you snap the shutter when the camera is pointed at something else, that's the image you will see; if you stop your engine operation at another rpm than the one important to you, the richness indicated by the plug reflects the last continuous operation state.

The Gordon Jennings article referred to you previously by another poster, plus carburetor tuning references appearing on the Forum, answer your questions.

Am I correct in my understanding, you own a DS with several thousand dollars worth of hop-up add-ons? If so, have you experimented with different sizes of relatively inexpensive carburetor jets?

Tree Farmer

 

The White Bros. web site has a page that will tell you exactly how to read the plug and jet your carb. I went there just browsing and I went to the install/ test of the E-series on a 400ex and a couple pages in it showed how to tune the carb for the new mod.

 

What I have found to be helpfull when setting the pilot and needle, is to limit the throttle travel so you only get about 1/2 to 3/4 throttle.
A BIG rideing area with a few hills and the least amount of ruts, will make things a little easier.

 

I tried reading the plug after idling, after dragging at full throttle and cutting the ignition, and at "random" when I have come to a stop. In all cases the plugs were exactly the same - it made no difference how I ran the engine prior to checking the plug. The only difference I have seen is when the engine is cold. Not thousands of dollars in mods, just RW STG I Kit.