HELP!! Plug Color

I am looking for some thoughts from the collective wisdom of the forum.

I have a '99 WR400 with YZ timing. It has the stock exhaust w/o the baffle.

Jetting: 48 Pilot, screw 2.25 turns out, DVP needle clip position number 5, 185

main (0 to 1500 ft alt). Air box lid is in place without the snorkel (helps

keeps water out). Stock sparkplug NGK CR8E.

The machine runs great - it is crisp and hits hard over the full range.

However, the sparkplug looks rather odd compared to what I have seen on other

machines over the years. The very end of the insulator, the tip of the center

electrode and the straight end portion of the ground electrode are white (even

though the tips of the electrodes do not look white in the scanned image). The

rest of the plug is very black with carbon. Color goes from white to very black

with no transition.

How does this compare to other WR plugs??

Thanks for any help or ideas you can offer.

Eric in WA

'99 WR400, YZ timing, IMS Tank, YZ Seat, Acerbis Handguards, Yamaha Full

Skidplate, Devol Rad Guards, Dunlop 755F & 756R Tires

'99 Polaris 400 Scrambler

'99 Honda Z50R

'97 Honda XR70R

Kubota L275DT and an assortment of farm tools.


Eric, how did you perform the plug reading check? (procedure of shutting down from the engine test run) The reason I ask is this looks like a condition of running rich for a period and then lean for a period. The needle clip position and main jet are much richer than most on the forum and you have left the air box lid on. The lid restricts and richens top end along with the main jet, but not bottom end. The low end jetting of 48 pilot. 2.25 turns, and "--P" needle are typical and could be the source of the white tip. Possibly on the lean side and burning off the carbon from the high speed run if you had maybe let it idle for a time. Stroker even says to use a 50 pilot at 0-4000ft.

This is an curious looking plug condition...

My plug looks just like yours. I've got a '99 with YZ timing, 48 pilot, 180 main, DVR 4th, E-Series 9 plates. I keep feeling like it running lean. One mechanic told me that due to all of the additives they put in pump gas these days, the plug will always look white.

A 185 seems really rich..... hows your top end?


its showing rich. almost fouled. the outer part adjacent to the chamber is where to read the mixture. of course it will show the mix at the last throttle position you were running at.


My plug looks the same as yours also. I am running a 180 MJ. The other jets match yours. I have removed the octopus and gone w/ Clarks jetting suggestions for that. My problem is my bike will never start in any condition w/out the use of the hot start button. I have closed my fuel screw to 1.5 turns. I have not yet completed assembling my bike to test it yet.



99 WR, 84 Kaw 900 Ninja, '82 Honda CB750F clothes hanger, '84 Honda Z50 "Berm Destroyer". Always thinkin' "Hell, this worked on my 2 stroke!!"

Thanks for all the responses.

To reply to some of the questions:

Altitude is about 0 to 1000 ft.

The plug looked the same when I cruised into the shop just above idle as it did with a full throttle run culminated by hitting the kill button.

About half the time the engine starts easily when hot without the hot start button at mild temps ~50-60 Deg F. Perhaps a larger pilot (50) as James suggested or going to the stock WR DTM needle would help richen the low end as James Dean had suggested?

Comparing the 180 to 185 main, the plug had slightly more carbon with the 185. Performance-wise, I could not tell a difference. In either case it runs very well throughout the range.

One remaining question.....What fuel are you using? Unleaded pump fuel or leaded racing fuel?

Option 1) It ain't broke, don't fix it.

Option 2) looks rich midrange to topend - 180 main, DVP#4, and lean down low - pilot #50

Option 3) DTM is richer on both clip and straight diameter so - 180 main, DTM#3, pilot #48 (similar to option 2)

note: too many changes at one time may be misleading, I like option 1 as long as it's running great.

Thanks for the thoughts on jetting changes.

I am using pump unleaded 92 octane with STA-BIL at 1 oz per 2.5 gal.

I will richen up the low end a bit as a first step - one step at a time.

Are there any detriments to the engine running slightly rich?


Eric in WA


’99 WR400, YZ timing, IMS Tank, YZ Seat, Acerbis Handguards, Scotts Steering Damper, Renthal Bars, Yamaha Full Skidplate, Devol Rad Guards, Dunlop 755F & 756R Tires

’99 Polaris 400 Scrambler –“Trail Couch and Lunchwagon”

’99 Honda Z50R

’97 Honda XR70R

Kubota L275DT and an assortment of farm equipment.

Mostly carbon build up and potential plug fouling. Fouling a plug in a wet mud bog on a rainy day is not any fun, from my experience. WA is known for these conditions making it a higher risk for you than most. See what others are using for jetting in the forum section on that topic. Most have main jets in the 172-180 range. DVR #4 or DVP #4 is most common for YZ's and DTM #3 for WR's. Understanding the codes using the clip position shown, these are identical past 1/4 throttle and DTM is richest 0-1/8, then DVP, then DVR is leanest 0-1/8. (reference last letter --M,--P,--R)

You are running too rich suggest the following;

With the 48 PJ go to 1.25 to 1.5 turns out

With DVP use #3 (perferred) or #4 from top 180 MJ max.

Remember a little poping on decelleration with good clean response everywhere else is OK.

This bike has a great tollerence to running in a rich condition right up to the point of "bam" a fouled plug. Plug readings are tough with unleaded gas and bike that runs a cleanly as this one.

Good Luck and keep us posted


Thanks Dr. Jet (aka Clark). I will inform you of the outcome.

I will be recieving a BigGun SDS sytem next week. I suspect that will require some further tuning.

Eric in WA


’99 WR400, YZ timing, IMS Tank, YZ Seat, Acerbis Handguards, Scotts Steering Damper, Devol Rad Guards, Dunlop 755F & 756R Tires

’99 Polaris 400 Scrambler –“Trail Couch, Toolbox and Lunchwagon”

’99 Honda Z50R, ’97 Honda XR70R, Kubota L275DT and an assortment of farm equipment.

Eric, I would agree with Clark on the jetting. It is worth remembering that the TPS adjusts the advance and retard of the spark according to load so plug colour as a guide is different to other bikes. The octane booster could also contribute, generel wisdom is that with octane boosters you need to advance the timing. Since the TPS adjusts the timing there may be situations where the burn is clean and others where it is not.

OK now this may cause some discussion, but I'll throw it out here. My plug looks similar, but not nearly as bad. It runs great too. I agree with everyone it looks like the jetting is rich. These bikes run well when rich, until you foul a plug in the foredescribed mudhole.

But I can't agree that only the white areas would magically turn from black to white so quickly during a plug test run. I would think that if the bike ran lean (starting and warm up or just small thottle) then ran rich (WFO test) and turned off with the kill right after wfo, the richness would show everywhere on the plug-not just what is shown above.

So now I am starting to wonder if the plug is borderline too hot. Around the edge where it's black is what the head is like and what the overall mixture really is-too rich. But the insulated and hottest part of the plug are burning the carbon off very well- a good thing unless they hot enough to glow and cause pre-ignition. Unfortunately trying and even hotter plug may be risky to to this, especially with the high-compression and TPS.

Am I crazy? Have a had too beers wondering about this? Someone, anyone--any takers to this theory??

On the other hand, it would make sense that Yamaha would choose a plug that would agree with most gasolines, riding conditions, and bike variances and satisfy the "not too cold to foul and not too hot to pre-ignite needs- so the weird multi-color reading may be normal for some bikes. Rich, Clark, James, et all- what are your thoughts?

mcarp-3 month WR owner and learning everyday.

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