Spark plug

Sorry to bring up this subject again but I have a 99 wr400 and the spark plug is showing white on the very tip and black around the outside, the ceramic part of the plug in the center is still white, there is no colour on it at all. I am running a dvp #4 175 main and 2 turns out on the screw.

I have tried a 178 main but this only made the outer part of the plug even blacker. I have adjusted the screw but this didn't get rid of the white tip.I am running a FMF megamax 11 exhaust with yz timing air box lid removed twin air filter with shell optimax fuel which is slightly higher octane than premium unleaded.The bike runs nice and crisp right through the entire range.I have notice the muffler gets very hot but the radiator has never boiled or overheated. Is it normal for the muffler to get that hot that if you spit on it, it will sizzle?

Does it sound like it could be the needle that is making the plug white and will putting the clip on #5 make it better or cause other problems? Or should i just leave it.I live in Australia and it about 16°c ambient because we are just coming out of winter and I ride about 0- 1000 meters above sea level.I have checked for air leaks and my hot start switch and they are o.k. I have read other articles on this site about people that have had the same problem but I coundn't find out what they did to rectify this problem . If anyone can help it would be appreciated.


The pipe on my 426 gets so hot that, in the dark, you'd swear it was translucent. But I would NEVER spit on my bike!

Just kidding. My silencer also gets hot, too hot to grab ahold of, but I don't know if it is hot enough to cook with...

That IS funny about your plug. I have always noticed at least tannish brown on the porcelain part, even after just one ride and even if I KNEW it was too lean (too lazy to rejet my first day at Glamis, 158 main in 426, plug was light brown).

Another tip I've read here is to do a high speed run, kill the bike and take off the silencer and read the color of deposits there much like you would a plug. Tannish brown being optimal, too light being lean.

Not the answer you were looking for I'm sure but I hope this helps you or possibly entertains someone else...

BTW, what plug are you running? Could a overly hot plug shield porcelain so much that trying to "read" its color is pointless? Boy I'm really reaching now...

[This message has been edited by Hick (edited 08-29-2000).]


Thanks for your reply

The plug I am using is a NGK CR8E.

If your WR has WR cam timing you may want to try the #5 or #6 clip postion to see if you gain any performance since your riding is in lower elevations from sea level to 3500ft.

If your are not experiencing any radiator boil over into the overflow bottle etc. I would not be too concerned. The plug center ceramic color near the tip is more a function of fuel selection than jetting unless you are way off. If possible try a magnifing glass and get a look at the procilin near the interface to the metal outside jacket down in the recess this is a better area to look at for plug readings.

But as stated last year with a clean running bike like the WR and excellent atomization of the fuels and no oil getting into the combusiton chamber around the rings or through the valve seals the plugs look great when they are taken out of this bike. Mine only color up when I rund VP fuels and the coloration is due to the color additive that VP used C-12 (green), VP red (RED) C-14 (yellow) etc.

I have not been able to jet at all on this bike by plug color only by performance, responsiveness, and radiator observations.

I would get real excited if you pulled out the plug and the porcelin, the metal tip and the metal base were all white with white/greay ash and or frequent radiator overflow action then yes way too lean but from you comment this is not the case.



Thanks for your reply and words of great wisdom

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