02 Wr426 - Black plug and popping above 1/2 throttle

Please Help... Just recently my bike started to really pop at mid revs... it then continued to do it at almost all revs on the increse and decrese... Lost power, then it would come back, lose it again.... Then I would LOSE IT... Pulled the plug and it was BLACK and I mean BLACK with heavy soot buildup on it. Assuming it is running rich or losing spark... Not really sure.. Not sure of jetting other than running a 165 Main and assume the rest is stock as I have never touched it. I put a new plug in it and it lasted about 4 miles before starting the same thing again. ran it Wide open all the way home and it's still the same.. I don't have a Freakin' Clue :excuseme:

I've searched posts, but have yet to find one with the same problems... BTW it is a Canadian WR - stainless pipe - no grey wire - no AIS (Smog crap)??? etc....

Thanks for any help..


You are running way too rich. Now that summer is hear the air is hotter which requires less gas. Drop the main down until it gets better, then fine tune it with the needle, then the pilot circuit.

If your bike has always run well with that jetting, I'd be looking at either a week spark or some reason for it running extra rich. Your not running high energy fuel are you? WR's hate that because it is denser and you need to lean off to be able to run it. Possible things to look for would be dirty filter, needle seated in the slide properly, slide in correctly, float level, carb breathers, overflow tubes not blocked etc.

I'm working nights tonight til 7 am tomorrow, so I'll pull the carb out and finally get down to see what's in it for jetting. I just filled up with Premium gas prior to all the crap, but with the price of premium being what it is lately, it's probably been in the ground for a year and stale. I'll probably drain the tank and carb, lower the needle and see about lowering the pilot jet.... Thanks for the quick responses.... I love this site.... I have not seen one that has had this many members anywhere else..


It may just be some water in the fuel. I had a similar thing happen to me riding in the rain on my KLX. Drained the carby and it's never done it again since :excuseme:

Well, I got to it... Drained the tank, dropped the needle (it was on #5 - moved it to #3... I know I read the manual, the numbers start from the top of the needle) also pulled all of the jets out and wrote down the numbers, blew compressed air through the passages, inspected the accellerator pump, the air-cut valve, etc. Didn't find any obvious dirt, or ANY for that matter . Put a NEW plug in it, NEW premium gas, and fired it up. I left the TPS disconnected for the first 10 miles or so, It ran like a champ, no sputter, burble, pop. Then I connected the TPS and it still ran great, well not super great, it seamed to be lacking some of it's crispness when trying to lift the front wheel in 3rd gear when cruising down the street. I may go back in and raise the needle one clip.

Here is my jetting


Needle OBDQR

MAJ 200

PAJ 75

Starter 65

Pilot 45

Pilot screw 2 turns out

Stock filter - snorkel removed

Stock Stainless pipe - Canadian Model

Stock valve timing

Stock ignition timing - No grey wire on Canadian Model?!?!?

If anyone else has a suggestion or two, I could sure use it!

I am Glad to hear that things are working better with a clean carburetor. Before you go crazy with the jetting you should consider some things like if you want more power or cleaner response the single biggest differnce will be made by replacing the Canadian exhaust pipe. Any name brand reasonably quiet slip on will make a big differnce. The BK mod was also very successsfull for me it really cleaned up low end throttle response. These mods are cheap after the BK mod you will need to rejet anyway. The Canadian carb needle is richer (better) than the US needle. search this forum for BK mod or Google it MOTOMAN 393 I think posted the BK mod on TT. As far as the ignition goes there are some tests in the manual (mostly no spark) you may check the coil wire and coil resistance and other stator coil resistance tests next time the tank is off just for fun.

You should have just changed the plug before doing anything. These bikes foul plugs regularly.

You should have just changed the plug before doing anything. These bikes foul plugs regularly.

Thanks for your advice, but I have changed about 6 plugs in the last 4 months... When I took it out and it was BLACK..... I tossed it in the garbage and took one from the 2-3 that I keep on hand and put it in... As I said above, changing the plug did nothing... It was the same in about 5 miles or so.... that's how I knew something ELSE was wrong...

You should have just changed the plug before doing anything. These bikes foul plugs regularly.

If your bike is fouling plugs regularly then you need to do some work. I have replaced 1 fouled plug since I bought my 02 in early 04. This plug was just wet fouled, and I threw a new one in there just because I hadn't changed it before. I disagree with your statement, I would not say that it would be normal for any 4 stroke bike to foul plugs on a regular basis. Just my 2c.


I knew I had problems.... The first couple of plugs were wet fouled (getting used to starting the big brute and people TWISTING THE THROTTLE on my new bike), but a couple were fouled from driving it... I had asked the question to a couple of people here through TT and was working it out, Then it got REALLY bad.... Since I cleaned the "No Dirt" (Could see no visible dirt) from the carby, dropped the needle, and checked the float level, All Has Been Well... The one good thing is that I now know exactly what is in the carb for jetting, so when I ask someone what is the best thing to do for any problems I may have, I can tell them what I'm running.... I appreciate your help as well as EVERYONE else.... THIS SITE IS AWESOME :ride::ride::ride:

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