Accelerator pump problems

I just did the bk mod as seen on motoman's web page(great pictures of the mod). Everything went great but I noticed another problem. The accelerator pump will not pump. It seems that the top spring is too weak or the pump spring is too stiff. With the cover off of the pump, I put my finger on the diaphram and opened the throttle and the actuator rod works fine. But once it is back together it doesn't work. It can be easily moved by hand once the throttle is opened, and nothing seems to be in a bind. I've tried it on the bike, off the bike and with the bike running and still no luck.

Has anyone else seen this problem?



2000 WR400, all the free stuff

Yea, at least on my '98. You've got to keep all of the pivot points of the actuator and linkage clean. The most friction builds on the shaft that holds the bellcrank and spring. It runs through the width of the carb.

Carefully take it apart, clean all of the moving parts, and lubricate with a dry lube like graphite or teflon. Dry lube for gun actions is what I use, it won't gum up with dust like oil will.

That isn't the problem. I've checked everything for binding and there is plenty of tension. It moves easily until it starts to push the rod, that is when it stops. Like I said, with the cover off the pump it works the diaphram with a good deal of force. I think I'm going to try softening the pump spring.

By the way, this problem could have been here since new. It has always had a very bad bog when the throttle was snapped even to 1/3 open, and the pilot screw has never had any effect short of closing it completely or removing it altogether.

I am currently using a 48 pilot, 100 air and 168 main with EKN on #3.

Thanks for your sugestion.


If you figure out what is causing the bog in your bike,I would greatly appreciate the info.I own a 1998 streetlegal wr400, and I have the same problem with mine, and cant figure out what is causing the problem.The carb was apart and cleaned inside and out and the accelerator pump was adjusted and nothing seems to help.Pretty annoying when your trying to dice with your buddys and you come into a corner and want that acceleration, and it falls flat on its face, and then all of a sudden comes back with a vengence.

Have you checked to make sure the pump circuit is unobstructed? A little carb cleaner in the proper hole in the cover should come out the bottom, and some into the proper passage in the carb body should easily squirt out the APJ.

Since you have covered everything else on this very simple apparatus that circuit blockage must be the problem.

Hope this helps.

hmmmmm, i'm sure someone here has sat down and worked on this problem. frustrating, hey?

Thanks for the replies guys. I haven't touched the bike in a week. I've been practically bedridden with this crappy flu thing going around central PA.

Any other suggestions are welcome.

Thanks again,


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