Plug Fouling Continues

Hi guys,

I am still chasing the plug fouling gremlin. Does anyone know how critical oil level is on a WR400?

My level was a little over full so I drained some out. It hasn't fouled the plug in about 30 minutes of riding but I can sure tell it is lean. It does not run as well and pops on decelleration. I will continue riding and testing over the weekend and report back Sunday or Monday.


Hi everyone,

I'm having about the same problem as Roger here. I ride a WR 400 -98 at about sea level. I have measured resistance at the ignition coil and plug cap and everything seems to be fine. The spark from the plug looks OK. The cams are on standard timing (I've checked of course). I have experimented alot with different plugs and the plug sometimes takes longer time to foul if I use a CR7E but it will foul eventually. In the summer they last longer but in the winter (-10 celcius) the plugs foul very quick. My fouled plugs are all black and sooty. I have experimented with different main jets (even extremes like 132 up to 190) but the plug will be black after like 10 minutes (wintertime) anyhow. In summer I can usually use the same plug for a couple of hours of riding.

I will disconnect the APJ according to the description above during the weekend and have a try with that. One thing that is a bit surprinsing is that I can turn the choke off after just a couple of seconds of running even if it's -10 celcius. Any ideas about that? Could it be way rich on the pilot jet?

The bike runs great until the plug fouls by the way. It doesn't smoke or anythink like that.

Will it be worth a try to fit a YZ 426 -01 carb on it by the way?

Any ideas would be greatly appreciated, the bike has been like this since I bought it (used) 2 years ago.

I had this prob with my old wr, But it was my fault!! Make sure your oil is not over filled. If you check your oil before the bike is warmed up it will register low. I over filled mine and had fouling problems. Could be the same thing you are having!!!

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