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hesitant off idol: is this normal on 250f


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It is a four stroke thing and it is "normal" for these bikes from the factory but it can be imporoved with a little tuning. Do a search for BK mod, leak jt mod, and accelerator pump and you will find plenty of ways to approach this problem. Few have completely cured it but many have improved it signficantly.

First make sure your pilot circuit is jetted properly. I also used a P-38 (instead of BK), adjusted my AP timing per manual, and went to a #40 leak jet. I have no bog at all when riding. If I put the bike on the stand it still bogs but that's because there is no load.

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My bike does it too, but only if you really whack it open off of idle. I don't care though, reason being the rest of my jetting is perfect, so I don't want to mess it up just to eliminate a minor annoyance. Besides, as I mentioned earlier, that's so low in the rpm range you don't use it while riding.

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Are you saying you can go from idle to WFO without a hiccup? I don't believe that. I've seen certain bikes do it worse than others, but never any that didn't do it at all. My bike is pretty good, but if I wick the throttle fast enough I can kill it. That is when it's sitting still. If I'm under way I've never encountered a problem. At least not one I can remember.

I think people get to wrapped up about trying to wick their throttles open with no bog. It's not going to happen on a single cylinder 4 stroke. At least not in my opinion.

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Definitely check into the accelerator pump mods.

If you are in fact wicking the throttle right off idle while the bike is on the stand, well just stop doing that. ๐Ÿ™‚

But, many have reported a definite bog (perhaps better described as a hesitation) that occurs when blipping the throttle at lower RPMs while rolling. Some don't seem to have much issue with the acceleration bog on their stock bikes. But, many have reported good results from tuning the AP a bit.

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Yes I can wick the throttle WFO and it will not bog. Both bikes that will do it. They never have bogged, burped, bitched, or anything.

They both hesitate when they are first fired up before they are good and warmed up. But once they are fully warmed up, they rev great.

Have you listened to the wav on the yamaha WR page? It doesnt bog either. Go figure. ๐Ÿ™‚

Granted for so many to say theirs does, there must be an issue. It may be that the AP adjustment is very sensitive, and having 2 different ways to affect it doesnt help much either.

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YZ250F Rider

I haven't found a bike yet that won't die if I snap the throttle open as fast as I can turn it. You haven't touched either bikes AP/leak jets/ or jetting IIRC. You have 2 "one of a kind" bikes my friend!

If I lived in Florida I would buy you a beverage of your choice if I couldn't bog/kill your bike with a quick wick of the throttle. Since I won't be in FL anytime soon are you coming to OK ever? ๐Ÿ™‚

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I know what you are talking about, YZ_Abuser. I can easily shut my bike down while it is idling in neutral by a very quick twist of the throttle. Actually, I didn't think it would kill so easily until someone else showed me.

While getting ready to ride, a buddy was asking me if my bike bogged off idle. While sitting on the bike I showed him that I could rev it right to the moon with no hesitation whatsoever. He reached over and gave it a twist and sure enough it died instantly. Seems that I instinctively do a very slight almost imperceptible roll on before grabbing the whole WOT. Didn't even realize it.

Now, of course, my second reaction after HUH? was "so what." I doesn't behave like that once I am rolling and I wouldn't dare try it in gear from a dead stop. :D

So, I think we are talking about two different things. The vacuum delay is obviously a characteristic of the motor or we wouldn't need an AP in the first place. I think the real issue here is that each stock bike seems to vary a little bit as far as how well the AP is initially setup and some notice a true hesitation that does not exist on other bikes and can be made to go away by tuning the AP. Also, the hesitation may be more or less apparent depending on what type of riding you are doing and what you expect to happen when you give it the gas. ๐Ÿ™‚

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