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boring out a 4-str carb?

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A friend of mine asked if boring out a 4-str carb got the same or similar results as boring out a 2-str carb. He just picked up his 05 CRF450 and can get the carb bored out for free, so he was asking.

I told him I thought so, but I am not sure. Has anyone done this, and if so, what kind of results did you get?

Thanks.

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Unless your name is Ricky, Chad or Kevin you are not riding your bike to it potential anyway.

Leave it alone and learn to ride it.

To answer your question:

Smaller bore carbs tend to give better low end response, but restrict high rpm running.

It's the other way for Big bores.

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i used to think as above that a 39mm might give away to gain at the top if bored to 41mm. however a top tuner-dale lineweaver-says that the 39mm carb was made for only 250-300cc multi cylinders and therefore a bigger carb would be good.

my info is that the body is used for the 37, 39 and 41mm carb. if you bore it out would you let us know here how it went?

i'm not sure what you'll do with the central 'loop' of aluminium that the slide goes over. it must be fragile?

if you do bore the carb you should do it off centre so that you take nothing from the base of the carn and only 2mm from the 'roof' and 1mm from both left and right.

it'll be interesting to see how you clamp the carb.

jetting will likely go up +5 to +8 as a safety precaution.

i'd expect just 1 bhp advantage as i believe the ports will be restrictive and not the carb. dyno before and after? gotta be worth it if you're doing it properly.

regards

Taffy

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