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Davey762

07yz450. Bogs/dies when throttle wacked open, no prob w/choke on. Ideas?

7 posts in this topic

Hi guys,

My bro recently bought a used 07 yz450, bike runs well and is in great shape aside from one little problem. When going slow enough, or low rpm in any gear really.... the bike will bog out, die when going from pretty much 1/8th throttle to full throttle or almost full throttle. Yet, it does not do it with the choke on.... which leads me to believe the bike would need a larger pilot jet, correct? Also thinking larger pilot because the bike pops pretty bad on deceleration.

Also, the bike has a full fmf exhaust system, sunline fuel screw as well. Tuning the fuel screw has had little affect on the problem, but like I said, the problem goes away with the choke on.

Thanks,Dave.

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Decel popping can be either an air leak in the exhaust system, or a lean idle circuit. Eliminate the exhaust first, then consider the pilot.

Check the jetting specs thread at the top of the index for this forum to see if anyone with a similar '07 has posted.

Also, don't expect any 4-stroke to be able to tolerate having the throttle "whacked open" without a protest. Learn to roll the throttle open more smoothly (not more slowly). Trying to "fix" this completely through jetting and AP mods will give you a bike that's way too fat on the bottom.

Read:

http://www.thumpertalk.com/forum/showthread.php?t=327405

http://www.thumpertalk.com/forum/showthread.php?p=3710599#post3710599

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Thanks for the reply. I do understand 4 strokes generally do not like to have the throttle opened very quickly, but it doesnt do it whatsoever with the choke on, so I'd at least like to acheive response like that.... or somthing more acceptable than what it is.

Also, I've ridden two other 07 yz450's and they both did have a bog worse than my crf... but still were both better than my bros. I will read up on the topics you posted and see what I can conclude, thanks.

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I do understand 4 strokes generally do not like to have the throttle opened very quickly, but it doesnt do it whatsoever with the choke on, so I'd at least like to acheive response like that.... or somthing more acceptable than what it is.
That would be nice, and it is achievable to some degree. But I think you'd agree that although the throttle response may be great with the choke on, the performance is otherwise not acceptable in that mode, which was what I was getting at.

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sounds like it needs some carb cleaning and jetting help to rid of most of the bog.....search for other ways to rid of it.

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Your 07 shouldnt bog when you get on the gas like that. It should be able to pound out from low throttle input to full.

But treating the throttle on the yzf like a 2 stroke is trouble!

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