plug fouling HELP!

i have a 98 wr 400 and lately the spark plug has been fouling as of used to be about 20 rides before a plug change, now its twice a ride.the bike will run great for about 10 laps then it will start to pop on decel, then hesitate on accel, then run like sh*t til i change the plug.I'm running 93 octane pump gas.

the plug is totally black when i remove it...too rich???

should i adjust the feul screw? if so which way to turn ? in or out?

the engine was totally rebuilt last year and the bike has performed perfect until now.

Can any of you guys help me?

Hmmm....sounds way rich....I doubt a fuel screw adjustment would make much difference to your problem....but if you want to fiddle anyway turning it INTO the carb will lean the setting.

Did something happen recently to change the jetting specs ?

- new gas type ?

- colder weather ?

- could be you have some blockage in one of your air jets...did you recently run in some high dusty environment ?

Anyway, take the carb apart, clean all and blow compressed air throught all the jets (be carefull of the washer & spring in the fuel screw recess...make sure you have them in your hand before blowing air into anything !

- bk mod malfunctioning ... ??

Your symptoms sound identical to my 426 about 6 months ago. Turned out to be a contaminated batch of fuel (water). Drained tank, fuel bowl, and fitted CR8IEX plug, no problems since. :)

i did have a bad batch of fuel and have replaced with fresh gas.(93 octane)...the gas is good. we have been in REAL dusty evirons. i will do the filter/carb clean, then see where we are.i hope it could be something that simple.this bike never let me down before.

another question...last spring i was doing some woods riding and got a branch wedged agaist my engine...when i pulled it away, the wire that goes in to the spark plug cap came out...i just pushed it back in... since then i have done dozens of rides. Could that be a contributer to my problem? maybe the connection is corroded or arcing...causing a misfire fouling the plug...

whaddaya think?

Chris Startt

Check it out it isnt that big a deal if you are already messin with the carb

Sounds like a fuel issue, try VP ultimate 4 race fuel. I had trouble with my 2001 426 and with this fuel it runs great.


Did MD recently start mandating oxy fuel in your area for

this time of year?

I have had more trouble than you'd believe running oxy fuel

in my '01 YZ426. I switch to race gas in the winter and the

problem goes away.


Ditto. Oxy fuel would foul my 426 in 5 to 10 minutes. It was a complete pain in the @$$.

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