250f - bogs on open throttle

[rockchucker]

If I whack the throttle wide open the bike bogs momentarily, guess that's the "4-stroke cough" syndrome but the bike doesn't do this if you accelerate smoothly. Is there a way to cure this without having to purchase mods? Would adjustments to the air/fuel screw make a difference? I heard rumors of the carb slides coming out of adjustment on the 426's and caused this problem but then again this was told by a local dealer and don't know how reliable the source is.

 

[IBWFO]

Hey you OLD Sandbagger!!!!! LOL!
Check out the "Thmpertalk" site. www.thumpertalk.com
Very educational. On the 426 they do something called the "BK" mod.
Don't know if they do it on the 250.
Might be at VC Sat night or Oak Hill on Sun. You?
I see the doc on Friday, and hope he lets me out of this damn cast.
try this:

http://mx393.tripod.com/carbinfo.html

D

 

[ThumpinByYou]

thumpertalk extensively goes over the BK and p38 mods for both the 250 and 426. Just run a search, one of the guys even has pictures and detailed instructions on the BK mod, I believe his name is motoman358 or something of that sort.

JB

 

[yz250-effer]

Sounds fairly normal?

IF you really open the throttle fast ( to full open ) that sounds normal. I am no expert mechanic by any means, but it seems to me a 4 stroke can not consume fuel as fast as a 2 stroke since it only fires every 4th stroke. So when you crack the throttle real fast when the bike is not under load, the rpm's and fuel consumption may conflict. ( bog out and run too rich for the rpm). I have never felt this on the track on mine and that is all that really matters to me.

 

[rockchucker]

IBWFO - So you did break your arm that day at VC???? Man that really sucks!! I probably won't be at VC Saturday evening as I have a wedding to attend. I'm considering VC on Sunday, never been to Oakhill so maybe I'll give that a shot.

The bog is and isn't somewhat normal. It's always had it but the past few weeks it seems noticeably worse. It is difficult to wheelie effectively because the motor bogs. I've seen the post on the P-38 and BK mods. I'm thinking the BK mod would be best as a few people complained the P-38 didn't solve the problem. However drilling on my carb doesn't really excite me much either. Anyone think going up to a 45 pilot (stock is 42) might help? David - Did you do this mod on your 426?

D - hope your arm gets to feeling better.

 

[IBWFO]

Have not done it on mine, but on a buddies that I ride with.
It is really easy to see if you need this by removing the sub-frame and watching the gas squirt into the carb. We did my buddies YZF right after I got the CR.
It made a HUGE difference in throttle response!
Let me know if ya want some help doing it. I have the tap and all the tools.
The kid wants to race at Oak Hill on Sunday, so that is where we will be.
Cool track great soil. I fractured what is called the "Radial Head". It is not nearly as bad as actually breaking the arm. I see the doc Friday, and hopefully he will get me out of this cast, as it's a real bummer having a new bike and going to the races and only being able to watch!
C-ya soon