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I bought a 2005 yz250 off Craigslist, ran awesome! Took the bike completely apart Down to frame, did not touch motor just put it on my bench! Had frame powdered coated and put 3k in new parts to make it how I wanted it. I put pro circuit pipe and silencer  and changed fuel bowl gasket and that’s all I did on motor! Put everything back to get and it fired on second kick after 8 months of sitting! Went to buddy’s to ride it and you when you get to the powerband and starts cutting out or struggles! Jetting is from Pro Circuit recommendations page , 40:1 mixture with vp 110 fuel, put new reeds in, checked power valve and looked and moved good! Anyone have any ideas! 

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Posted (edited)

Did carb sit around for 8 months with fuel in it?

Did you check/set the float level for proper height?

Why are you running VP110 fuel? The engine stock compression ratio isn't high enough to require such high octane fuel. Running such high octane when the engine doesn't need it will make less power, is less efficient.

Pro Circuit jetting recommendations are just a starting point.

You have to fine tune from there for your elevation and conditions. If you'll post that info along with the current jetting you're running, you might find someone running nearly the same setup, with some suggestions.

Edited by Trailryder42

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Carb sat with nothing in it for like 8 months ! Ended up doing a carb kit after figuring out it ran like crap! Floats are good, and pro circuit told me to run 110 cuz of the crappy fuel at the pumps now days! The only thing I changed was put pro circuit pipe and silencer! I never changed jetting, motor ran very strong before I took bike apart to restore, someone said the power valve is sticking or bad? 

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It would not be unusual to need to tweak jetting after doing a complete exhaust swap.

I think Pro Circuit is wrong to tell you to run that VP race fuel. 91-93 pump gas will run fine without the extra expense and hassle of buying race fuel. You also can buy non ethanol. Check out pure-gas.org for a location near you.

https://www.pure-gas.org/extensions/maps.jsp?statecode=OR

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