'00 400 EXC chokes on Fast Roll of Throttle


Jul 4, 2001
Who has a '00 400 EXC that chokes or bogs down when the throttle is twisted pretty fast. Surely for the praise that this bike gets, this can't be accepted. When the RPM's are up fairly high I have no problem. My wife has a '96 XR250 and when you roll the throttle it responds perfectly. What is the diff? Somebody please enlighten me.


Damn Yankees
May 14, 2000
There are a couple of remedies; personly I never had that problem with my 520, but have heard from others hear that jetting, idle mixture, and exellerator pump adjustments can all contibute to this. Hang tight and somone will give you the proper proceedure.


Sep 6, 2000
All the 4-strokes with the Keihin carb have some hesitation right off idle, especially if you whack the throttle open.
Don't expect that any 4-stroke will have the throttle response of a two stroke, it just can't happen. The best remedy for the hesitation, is to turn the idle up a little, and put a p-38 on the carb. Also make sure that your bike is jetted properly, and that the accelerator pump pushrod is adjusted properly. Another thing is that the 400 will have a much more pronounced hesitation than a 520 simply because it doesn't have the torque like the bigger bike. Make sure to remove the crankcase breather from the side of the carb and plug it up. re-route the breather hose to vent out behind the carb or into the airbox. If you read the magazines and believe everything they say, they always say to roll the throttle on, on a 4-stroke. I say (as well as many other mx'ers I've talked to including some pros) that you need to use a little clutch sometimes (on the 400 especially) when accelerating through turns. My expert and pro mx'ing friends use their clutch alot more than I originally thought. Then again Barnett, and Z-racing sponsor them,
so money isn't an issue. They go through a clutch about every 6 to 8 weeks on their 520's and every 3 to 4 months on their 400's. Us average riders
probably can get an easy 2 years out of our clutches on the 400's and less of course on the 520's. Erik


Jul 4, 2000
THe first thing to check is the accell pump.Dirt gets worked in between the little rubber cover and the pump rod. Take it all apart and clean very good. If this does not cure your problem,turn your idle up to 1850 rpm. One of these two things cures 99.9% of the hesitation.

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