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Science Experiment

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Ok here I go. 98 XR 400R its getting a Wiesco 88mm 11:1 compression  big bore kit, new valves, guides some mild porting work. It has a two brothers pipe already on it. Gonna use the stock cam Has anyone out there done these mods and have jetting suggestions or parts suggestions. I'll take them all into consideration. I'd like to use slide carb but after the rest the wallet will be in sad shape for a minute. Thanks Doug

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If the carb was jetted properly before the big bore and mods, I suggest starting with that same jetting after the rebuild. It's not going to change much at all. The increased displacement creates higher negative intake pressure and vacuum signal on the same jetting.

 

At least, that's been my experience.

Edited by Trailryder42

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If the carb was jetted properly before the big bore and mods, I suggest starting with that same jetting after the rebuild. It's not going to change much at all. The increased displacement creates higher negative intake pressure and vacuum signal on the same jetting.

 

At least, that's been my experience.

 

I agree.  More displacement and/or more efficiency equates to more air being moved and more signal across the carb.  Start with what you had (if it was right) and go from there.

 

I use Mikuni's Roll-Off method to get my mains dialed in.

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