Yamaha WR400 2000 Model. Bogging Issue

Hello all I hvae just bought a 2000 yamaha wr400. Fancied one after reading the mag actually. So decided to buy a 2000 model just to smash up green laning in the winter months. Problem i have is that when u pull away fast. (give it a handful) it boggs right down and stalls as if it's flooded itself. I have done the basics cleaned air filter changed plug etc. But I did noticed that the return throttle cable is freyed very badly. Would this maybe be the cause? I noticed also that when u open the throttle fully it gets stuck then after say 2 seconds returns again. Any ideas you helpful bunch?

Well, first you want a bike with all systems in apparent proper operation. But doubtful that is the source of the bog. More likely either he AP is not working (clogged spray nozzle, broken AP cam or ruptured diaphragm) or it is poorly adjusted (wrong leak jet, bad AP timing)

Cheers for the reply William. Is there an easy way of checking the AP is working? Someone told me you can adjust this...Do you no how I go about it?

Move the airboot off of the carb.. Wear safety glasses. Look in the carb, nail the gas, you should see a good stream. I assume you have a leak size between 40 and 60, if you are not sure, check, change i needed.

If you have a good stream, you need to adjust the AP timing screw (next to the throttle wheel) 1/2 turn CCW, test ride. SAhould not need more than 10 minutes to resolve

have a 2001 wr400f and when it gets hot it stalls and won't start till it cools,major drama when half way up a hill in mud.....any ideas?

Does the 2000 model have a leak jet? I didn't think they did. But like William said, the basic cause of the bog, is bad accelerator pump timing. Check for a squirt, and guesstimate the time duration of the squirt. Do a search on "BK Mod" and adjust your squirt duration as per the mod, and you should have it running much better.

Thumpsterman, An alarm bell went off when you asked your question! When was the last time you checked the valve clearances? My guess is that they are tight, and are causing your issue. Check them now!!! The engine has to be completely cold, so check them first thing in the morning before trying to start it. Hope this helps.


I also have this issue with the same bike, I recently bought mine as well and am still working out the kinks. The bog is very troublesome when I need a quick burst to pop a curb or log or something, because instead of it raising the front tire when I need it to, it bogs out and gives me no gas making me nosedive into whatever it is.

A neighbor of mine though is giving me his Yoshi pipe from a YZF 250 and I know I'm going to need to do some rejetting so I was kind of putting it off. Do you guys know the amount it usually goes up when putting on an aftermarket pipe? I've found a guy with the same bike that lives in the same area on the jetting database, but he has a stock pipe I believe and hasn't signed on in forever. Is there a general number that it usually goes up? I think the pipe leans it out, so you'd need to go up a couple, right?

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