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CRF250X 280BB Porting?

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Hello, I have decided to purchase the Athena 280CC Big Bore kit for my 2006 CRF250X, I was wondering what exactly porting would do and if I should do it when I get the kit. Thanks!

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Your bike will run almost perfect....I needed a bigger pilot jet(45) for a smoother running low speed and I used a bigger main jet ...I think I went from a 160...to a 172. I don't know if porting will help much as the carburator will only flow so much. I guess it would maybe help midrange ,,,but wait until you install the kit.. Its quit a bit more powerfull. Specially if you ride off the mx track where torque and smooth power are your friend. You will lose some overrev and top end power.....not that much though. You will notice you have two more gears to use riding....4th and 5th are actually useful gears with the bigbore....Good luck....

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I was wondering if I should do it when I have the whole engine apart and how much it will cost, I know it helps the airstream or whatever and would improve throttle response, but has anyone else done this with their Athena BB kit? Thanks!

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just use a longer cam, most everything you read about porting and different year heads etc pertains to filling a 250cc hole efficiently at rpm. All bets are off with these mods at 280, and the rpms you'll run it at.

If you want a fast X, leave it a 250 13.5 piston and 08 cam are most cost effective. If you want grunt and pull and more lug and chug, do the big bore.

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I would consult the known engine builders directly on this. porting may be effective but it would have to be done right to work with your specific combination.

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Call Ron Hampe for his advise. The larger bore actually unshrouds the valves allowing better flow. Usually the stock 2008 Honda 250R cam works extremely well with a big bore, is cheap, and doesn't require any special springs and you know the quality is good. Cutting the air box and all the other free mods should be done along with proper jetting of course. Have fun!

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