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Crankyz450f

08 YZ450F miss firing

4 posts in this topic

hey guys,

I have a new YZF and have noticed that when im on the gravel roads between the tracks that we have it miss fires a lot at any constant engine speed.. It doesnt seem to affect it once im on the tracks but is really annoying tryin to cruise between them..

Is it jsut because they are such a high perfomance engine?

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Mine did something similar I don't know if I would call it a miss fire more like surging usually with a drop in power (not an increase). I went with a larger Main Jet, raised the needle one spot and that helped it a lot. Then it only did it when the throttle was barely open. So I went with a larger Pilot Jet and now it is fine over the entire throttle range. Starts easier too. Don't know if it is was that change or I just figured out how to ride a 4 stroke but I haven't stalled it in the corners since.

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Go 1 step larger on the pilot jet, trim the idle mixture correctly, and see if that takes care of it. There may be no need to enlarge the main or raise the needle (and so no benefit from it).

If it makes it worse (very doubtful unless you're at very high altitudes) then go down one.

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I have an 08 YZ 450 and it popped on decel and I checked the hot start lever play and it didn't have any! So I adjusted it to have just a little and it cured my popping altogether!

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