Engine dies when abruptly applying throttle

Just got a 2008 WR250x.

When I abruptly apply the throttle, the engine dies. If I slowly roll on, it revs up as normal. If you abruptly apply the throttle with the revs already a bit higher than idle, then it hesitates but does not die.

The previous user has a FMF power programmer with a FMF Q4 full system. I thought I might have changed the settings by accident and caused this, so I disconnected the programmer. It's still doing it.

I can fix things if I know what the problem is...but I have no idea what's causing this.

Any idea where to start?

Thanks!...trying to get this going for some ice racing this winter!!!

Does it do this while actually riding the bike?

YZEtc wrote:

Does it do this while actually riding the bike?

It does it while in gear at a stand still (clutch in, obviously) from idle.

I don't remember exactly what happens while moving, but i'm pretty sure it does. That's only when the throttle is abruptly opened from the full closed position though. I'm pretty sure it's okay if the throttle is say at %30 then abruptly opened. A slow feed and it's fine.

I'll have to double check how it reacts while riding though.

If it works fine while riding, it may be normal.
If it hesitates or cuts out while riding, not normal.

This definitely isn't normal. I've never had a bike, either carbonated or EFI, that has dropped RPM and dies when you quickly snap the throttle open.

Sounds like it is too lean at idle.....maybe adjust the CO settings (search the forum on how too). It is possible somebody messed with it and leaned it out to much which would cause that issue.

CRFan1 wrote:

Sounds like it is too lean at idle.....maybe adjust the CO settings (search the forum on how too).  It is possible somebody messed with it and leaned it out to much which would cause that issue.

Thanks! I'll look in to this and report back.

If you find a problem and fix it, come back here and post the reason and results.

CRFan1 wrote:

Sounds like it is too lean at idle.....maybe adjust the CO settings (search the forum on how too).  It is possible somebody messed with it and leaned it out to much which would cause that issue.

+1. Exactly what to expect if too lean.

I would also check your idle--my WR was prone to stalling in general until I turned the idle up a bit. I don't have the spec in front of me but the WR idling at spec sounds a little fast to me.

-morgan

Lean often gives an errativ high idle, where rich (also) makes it stumble. A bike that is rich in the low register, will idle worse when warm

Do the basics with fresh plug, newly serviced airfilter ect, before you try to diagnose the problem.

Is there any faultcodes logged in the computer?

Just read through this. Did the last owner remove the air box flapper and vacuum motor for it? There's a small hose that controls that, and it attaches to a nipple on the intake between the throttle body and cylinder head. If that's open, it's a vacuum leak. There's supposed to be a vacuum plug installed when you remove the air box flapper control. Even if it was installed initially, they tend to crack with heat and time and will then leak. If the flapper is gone, I'd check that brass nipple first and make sure there's an intact cap on it. It's hard to see, because it's up high and under the fuel tank (on top of the adapter that bolts to the head).

Anyone know what the issue was? I am having the same problem. My big gun exhaust broke ( the perforated pipe inside it broke. I temporarily welded a straight pipe inside of it. So 1/4 perforated pipe and 3/4 straight pipe). It was running fine for about 60km. It was just louder. But then I stopped and when I snapped the throttle, it hesitates and dies. If I slowly get on it up to full throttle, it's fine. Bike is currently in Africa so parts are a bit scared. Any help would be much appreciated.