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09 yz250f jetting with a DR.D exhaust?

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The settings were stock and had crappy throttle response at 4,000ft elevation (idaho). When i put on the DR.D it was unbarable. The 09 yz 250f had no low end or mid range but would pick up eventually and then take off. im about to put on a K&N air filter and i hope that gives more air flow but if its running lean now i dont want to fry my piston rings. Does anyone know what size jet i should have and what notch on the needle to have it on? and could you tell me if it would run lean or rich stock with the exhaust and at this elevation?

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Aftermarket exhaust has a tendency to make a bike run slightly leaner. A way of finding the jetting you need is go the jetting sticky and search for people that live at your same alt and temp but it can be a pain in the butt searching thru pages and pages and pages of posts. The easiest way is getting a JD jetting kit and follow James's instructions. His kit is designed to run with an open exhaust. If you have any more questions just email him. He does live up in your area of the country (next door in Washington)

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The settings were stock and had crappy throttle response at 4,000ft elevation (idaho). When i put on the DR.D it was unbarable. The 09 yz 250f had no low end or mid range but would pick up eventually and then take off. im about to put on a K&N air filter and i hope that gives more air flow but if its running lean now i dont want to fry my piston rings. Does anyone know what size jet i should have and what notch on the needle to have it on? and could you tell me if it would run lean or rich stock with the exhaust and at this elevation?

You're running rich. Were it me, I'd go to a 40PJ, lean the needle out 1-2 clips and lower the MJ by 1 or 2 sizes. When you test this combo, roll the throttle on and test on an uphill climb in 3rd 4th and 5th. Rolling the throttle takes out the AP circuit. You can tune that last.

If your concerned about being too lean and burning up the bike, don't worry. You've got to be very very lean to burn it up and if it's that lean, it will barely run.

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thanks guys i rejetted it and now it runs like a champ through 1st 2nd and 3rd but 4 took a hit and my top speed isnt as fast which isnt a big deal but i was wondering why. i would destroy my boy on his 2 stroke which needs alot of work so its kinda a turd, but now his top speed is faster. could you tell me why? and 4th is lacking pretty bad and i forget how to change that.

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thanks guys i rejetted it and now it runs like a champ through 1st 2nd and 3rd but 4 took a hit and my top speed isnt as fast which isnt a big deal but i was wondering why. i would destroy my boy on his 2 stroke which needs alot of work so its kinda a turd, but now his top speed is faster. could you tell me why? and 4th is lacking pretty bad and i forget how to change that.

Odd. If 1st-3rd is better then 4th and 5th should be too. What are your throttle settings when this thing turns into a turd? Are you WFO on the mainjet or 1/2 throttle on the needle?

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