Intermittent Rough Running WR400

Ive got a 98 WR400, which I've had from new, only gets 30 hours use a year, so is still in good condition.

During the last couple of Enduros, I have noticed that occasionally the engine runs very roughly, Backfiring on deceleration, Severe bogging when the throttle is opened, only under load though. It's fine when revving in neutral.

It feels a little like it has water in the Filter, but that is OK.

It usually clears after a couple of Kms, and is fine.

One time it did it immediately after a big G-Out.

I have drained the carb, no change.

New Plug, no change.

Feels very rich, and then clears itself, and is fine for another hour or so.

I have wondered about the Filter screen getting blocked, but seems unlikely.

It occurs more often just after starting the engine. Even when warm.

I thought possibly the accelerator pump was not working correctly, but that would make it lean, not feel rich, am I right on that?

Will pull the carb this weekend, and check everything.

Another thing, this is a Euro model in New Zealand, and it came without all the restrictors-grey wire etc that the US models seem to have. Also the accelerator Pump squirt has from new only had approx 0.25 sec duration.

This bike runs really strong (except for this intermittent problem)

Anybody who can offer some advise would be appreciated.


Pete galpin

Kiwi Vet

Peter- a friend had similar probs with his 426. You might try a search here on de-octopusing the carb(I think thats what they call it :) Please, someone chime in if I'm wrong)). Anyway, as I understand it, the mod allows you to time the accelerator pump. His would squirt to soon, spraying the slide before it opened enough. Sometimes his bike ran good, others it would load up and run bad. Runs good now.

I recently had the same problem, I messed with the jetting for a month and it turned out to be an electrical problem. :) Mine was shorting out where the plug whire and cap connected. My bike would run fine until the engine heated up enough and the wire became more flexible and started to short. My point being check the electrical!

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