I recently bought a 2000 WR 400. I took it to the local riding hot spot and was very pleased with the bike. The problem that I am having though, is that when I try to really crack the throttle open, the bike stutter-steps. This gets very scary when you are trying to launch over a table top, and you don't have that last second punch. It also has a hard time idling. I took the bike home and checked the airfilter which looked fine. I asked a friend of mine what he thought and he said that if the previous owner had removed the baffles from the pipe, it would make the bike run differently. He told me to open the carberator and move the clip down one notch on the needle. I did this and now the bike idles great, and when I gradually give it gas, it runs fine, but if I barely try to crack the throttle it dies. Does this mean that I'm getting too much gas? Did moving the clip make that much of a difference? I am really lost here. If anyone could give me some sort of guidance, it would be greatly appreciated! Thanks! Luke

The February issue of Dirt Bike Magazine has an article that includes tuning tips for YZ450s. They suggest backing the accelerator pump adjuster down to reduce the stumble when snapping the throttle open at lower RPM. 1/2 turn clockwise on the adjuster is recommended.

Whether this will help a WR is unknown, but it's worth a try.

Sounds like you need to do the BK mod... Do a search on the phrase "BK mod"... look back maybe a year or so, and you should find plenty of info... also, you can go to http://motoman393.thumpertalk.com for more info on this as well...

Basically, your accelerator pump has too long of a duration, and is flooding the bike as you open the throttle quickly... you need to reduce the fuel spray from 3 seconds down to something more sensible... like a half second...

You may also have to tweak your jetting, to get it to run at 100 percent of it's capacity...

You may also consider the JamesNow Mod... www.just-ride-it.com/powernow.pdf That mod will get you some low speed pickup...

Look around the site and you will also discover that there are other mods you may want to do like:

the throttle stop,

the grey wire,

the airbox lid,

YZ cam timing - some of these may have been done before you got the bike, but you you can easily check...

Welcome to ThumperTalk, we will get your bike running right, just search and ask...


Would it be the Bk or P38 for a 2000 WR?

For the 2000 and newer WR its the BK mod.


Pull your carb. off so you can look in the back of it. With the fuel line and cables attached, twist the throttle. If your squirt is longer that 1/2 second you should do the BK mod. My previous bike was the 00WR 400 and there was no bog anywhere. Have fun.

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