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KTM 2 Stroke Big Bore Build

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Hi Guys.  I have recently installed a big bore kit (300cc) on my 2011 KTM 250 XC W.  I am having some issues.  Since I have done the modification, I am going through piston kits.  The bike has only done about 80 hours on it since the rebuild, but I am already on a Gr1 piston kit.  The bike seems to run very hot.  I have now installed an external cooling fan on the radiator.  I have not changed the carburetor jetting sizes, but I have changed the needle position - now position 4.  The air screw is set to 1.75 turns.  Does anyone have any advice?  Cheers. PaoloC

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Generally when you put a larger piston in with the existing carburetor your jetting needs go towards smaller jets.  Greater vacuum puts a stronger "pull" on the existing jets,  and draws more fuel through them.   My guess is your head work was not done right.   

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When you refer to "head work" not being done right, what does it mean and how can I do it?

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