WR 400 hesitation

I have a 2000 WR 400 and have recently done an exhaust insert change, air box mod, and grey wire disconnect. The bike always tended to "stumble" from idle to about 1/8 throttle and it hasn't really changed with the mods. Any jetting or carb mods that would remove this annoyance?

welcome to TT.

if you have done the air box and exhaust mods re jetting will be necessary. :)

Any jetting or carb mods that would remove this annoyance?

Do a search on this term: "BK Mod"

You may also consider a wholesale re-jetting now that it is uncorked/uncovered.

Hope this helps.

Someone else I exchanged an e-mail with suggested adjusting the pilot screw and checking the pilot jet since the problem seems to be from idle to about 1/8 throttle. Anyone have any experience with this?

Someone else I exchanged an e-mail with suggested adjusting the pilot screw and checking the pilot jet since the problem seems to be from idle to about 1/8 throttle. Anyone have any experience with this?

It isn't simple to suggest you some "universal advices" to help you: It's correct to adjust pilot screw and pilot jet, but how many you have to modify these set up it's depend from the mods that you have done.

bye

Someone else I exchanged an e-mail with suggested adjusting the pilot screw and checking the pilot jet since the problem seems to be from idle to about 1/8 throttle. Anyone have any experience with this?

You're going to have to bite the bullet and learn to jet the bike. It is easy, the bike is talking, you just need to listen.

So it has a stumble at about 1/8th. Hmm. What to do.

How about a long cruise in a tall gear at the same throttle position? That eliminates the effect of the accelerator pump. If the bike surges during this test try a richer setting, if it stumbles try leaner. Get it as good as you can. If it is really 1/8th throttle then the pilot screw should affect things, a good rule of thumb is that if you end up richer than 2-1/4 turns out, or leaner than 1-1/2 turns out you may want to try another pilot jet.

Now, once you have a steady-state situation worked out, if the stumble is still there when you twist it (likely) then you need to adjust your accelerator pump w/ the BK mod.

Hope this helps.

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