stalling with rapid throttle twist

Hi everyone, is it normal for my brand new bike to stall when at idle I twist the throttle really fast. I have never had a 4-stroke before and with all of my old bikes you can rip the throttle and the rpm's climb right up. My neighbor told me it is normal for 4-strokes to die when you do that. By the way, I am talking about when the bike is in neutral, riding it feels fine. Any thoughts?

My 00 does this until its warm occasionally.

I normally keep the choke out (Black Nobe) for a couple of minutes.

It has pretty much gone away since I jetted and BKmod the bike....

Its normal fo rthe yamaha but not generic to 4 strokes, thats were your nieghber is wrong

Is the engine hot or cold when this happens?

It does it when it is cold and at operating temperature. What should I do, I just bought this thing new 2 days ago.

If it is at operating temp and stalling like that then bring the idle up a bit more, that should help out

A buddy of mine in New York just bought a YZ250F. He's been complaining of a bog that he can't get rid does it when he cracks the throttle wide open from idle.

Strangly enough...I have never cracked my throttle WFO from a dead idle to see if it bogs...until yesterday.

I hit the throttle wide open and no bog and no stall. It rev'd all the way up smoothly..several time...

My bike had been warmed up and rode before I tried it. I know it will cough and die trying the same thing when the engine is cold.

Hope that helps ya.

Kirtwell, my bike does not bog at all, it just flat dies when I rip the throttle. I will turn the idle up a little bit and see if that helps, thanks guys.


Do a search for the BKmod, the 250 wil benifit from this fix also


Welcome to the brother hood. I also have an 02yz426 and I also have the issue of stalling when wacking the throttle and it dies. I never noticed any bog-off-idle either. However, I have been off a bike for 12 years and i thought it was running fine. I let let 2 friends ride my bike and both of them noticed a hesitation off of idle and what I have done is measure my squirt duration in the carb (last night w/ a video camera) because i have my bike torn down for suspension work. I measured approx. 2.5 seconds. I will be doing the bk mod this week to get it down to .3 seconds. Hope this info helps.

Ok, just got off the phone with the dealer and they said the pilot jet is too lean. He said "bring it in and we will handle it no prob" That was pretty good service if you ask me.

Question, being a two stroke guy, I might be off base but don't all bike come rich from the factory rich just to be safe? I wonder why my bike came lean?

[ May 09, 2002: Message edited by: yznvegas ]

Well, I have a Cannondale (quad) but I had the EXACT same problem with mine. It wouldn't idle good, if I hit the throttle it would die, and when I rode it, it would run OK but not top notch. I turned the idle up to where it sounds normal and now it almost runs like it should. I need to find someone with a tach so I can see exactly how much RPM's I'm running, but I'm willing to bet your problem is the idle.

Well, the dealer feels it is a lean pilot jet so that is what they are fixing right now.

I forgot to mention that my BRAND NEW bike has spewed about a 1/4 of a quart of oil out of the oil hose coming out by the left peg. What the hell is up with that, this bike is brand new, I shouldn't be having these problems.


You can get a bog from too rich or too lean. Burns says a bike properly jetted won't take full throttle when cold but should when warm.

A quick silent death on whacked throttle on stand is too little accelerator pump squirt. If that is it, if you put it in a high gear and go slow (starting to lug) and whack it, it will die every time. If this is the case, get a smaller leak jet. I've done lots of testing lately, probably had bottom of carb off 30 times in last two weeks.

You can mask this by (1) upping the idle or (2) enrichening the pilot or fuel screw but if (2) you are going to give up snap and low end power. Leave the circuit lean and let the AP take care of the loss of vacuum on whacked throttle. I think YZF stock is 100, try 80, 60, and 40.

If I'm right the BK mod will make it worse. DOC has posted another fix, plug the leak jet and adjust with BK mod. Try this if with smallest leak jet you still have the problem. It may be a good idea anyway.

If this is new to you, post back and I will give full details on testing it and how to change leak jets without pulling carb. This is NOT as big a deal as it sounds.

Good luck,


p.s., the newer carbs are way different from the early ones in that Taffy says to remove AP actuator for jetting. These carbs will NOT accept throttle leading much at all without one.


I am looking at page 1-16 of my '02 426 manual, and it says:

"Since this model is equipped with an accelorator pump, if the engine is raced (the throttle opened and closed), the air/fuel mixture will be too rich and the engine may stall."

My bike does the same thing, and I think it is normal.

Mark, thanks for the info. I am just starting to see the light on this whole jetting thing. I have to admit, it is still pretty scary for me because I used to have a cr-125 and I lean seized it because I didn't know what the hell I was doing. :)

I am getting the bike back tomorrow afternoon and I will let you guys know what the story is.

By the way, do you guys get a bunch of overflow oil coming out of that line by your left foot peg? I told the dealer and they said "Oh, we must have just overfilled the crankcase when we prepped it". Doesn't overfilling a crankcase bust out the seals on the engine? What are your thoughts?

Whats a bog ?

is this something i need to look for when I ride ?

maybe thats whats making me crash in turns

First of all a Thumper isnt quite as sensitive to jetting as a 2 smoke! You would have to get your jetting off pretty bad to sieze it. Anyway quit whacking the throttle in neutral! Put the bike in gear and ride it does it still do it? These bikes have plenty of power stock.The BK mod did help my starting problems and maybe crispened response a bit. Read the manual and do what it says about jetting. It is good information. Good Luck

You may be able to improve on it buy messing with the jetting, but the YZF doesn't like to be snapped instantly from idle to wide open (especially when cold).

Mine had a greater tendency to cough and die when it's was new (not broken in), but I was a two stoke rider before that, so maybe I needed breaking in as well....

[ May 09, 2002: Message edited by: holeshot ]

Holeshot, my bike does it at operating temperature too though. When I am running in gear and slow down sometimes the engine dies too. I know that is not normal.

You're right Ego,

In fact I turned him on to this site...he was totally impressed.

My buddy is reluctant to do the BK Mod just yet.

I think he's trying to get a fix by rejetting first. I guess he's a little weiry of drilling and tapping on his brand new baby thumper.. :)

I'll talk him into to it yet. 01 426 has absolutely no bog. I'd do the BK Mod on mine if I knew it needed it..but I don't think I'll leave mine alone.


If you want a second opinion on the "Lean" issue. Ask again in this forumn...These guys are the best tool you'll ever need...Personally it sounds like you're running rich to me....

just my .02

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