Help With '98 WR400 Bog

I am looking for suggestions on how to cure my '98's bog off of idle. I just returned from Utah and struggled on the extreme trails and some of the difficult trails. Maybe sending it down the road is the answer, I don't know.

It is jetted for Colorado, 5000' to 6000', sorry I don't have the jet numbers handy. I have them written down and will find them. I ride from Moab elevations to 12,000+.

It runs great until you get into tough technical sections then the problems start particularly when you have to finesse through tough spots.

So, smaller leak jet? Can I get an after market accel. pump diaphram for '98 WR400 with a longer stud to increase the squirt? I know I cannot adjust the squirt time so if there is a diaphram that does the same thing that would great.

Current setup: airbox lid removed, cam set to stock WR, stock exhaust - baffle removed. '98's are not supposed to have a grey wire however I did find one that comes out of the ignition switch, don't think that is the grey wire that needs clipped.

This bike is killing me in the technical stuff and as much as I love it, it may go down the road if I cannot get this worked out.

Thanks for any ideas.


Taffy Mod

Thanks Bamster. Where do I find info. on Taffy Mod? Google search?

See ya on the trail....


I have the exact bike as you.... I installed the JD Jetting kit along with a accel. diaphram that he had on his website for a KTM and no more bog......

Thanks for the info. CuLayTur. Do you know what size the post was for the KTM accel. pump diaphram? If not, no problem.

How do I get to JD's website so I can go look at what he has?

Thanks again.

See ya on the trail......


Hey Bamster,

I found the Taffy Mod. After pulling my carb. and testing the AP I discovered that the squirt from the AP does not kick in until the slide gets between 1/2 and 3/4 open. Even then it only lasts roughly a second. Which may explain why it really takes off when I am running about 30mph and whack the throttle, but bogs out when I am trying to finesse a technical spot and try to pop the throttle open a little which causes it to stall.

More testing needs to be done.

See ya on the trail...........


CoWr 400 rider

You need to search this forum for "Taffy mod" and "BK Mod" and do a lot of reading.

Based on the limited info you have both an Accelerator timing problem and an Accelerator squirt volume problem.

There is a ton of info in this forum on tuning accelerator pump systems. You should do the reading to gain a better understanding of the Accelerator pump system function. Did you read all the Sticky Notes at the top of the forum?

BTW you may need to rejet after Accelerator pump mods are made.

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