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just came across some old carbs and one pair was visibly bored out.  What is this technique called? anyone have a brief explanation.
 

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come on sledheads, someone must know? maybe its a silly question
but i need to know for a potential exhange
i know it draws more air and mixes with the gas and..............
 

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Carb boring, I don't know. I had Larry's in Orangeville bore a pair of VM34s out to 35.5 (?) I'm not sure of the top of my head what a Mikuni can be bored out to. I think it's slightly less than the next larger size.
 

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i wouldn't go any more than 2mm bigger      after that the metal gets too thin    better off getting bigger carbs
 

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I'm not sure I understand the question, But I think you are asking different boring techniques, right?

We do 2 types of bore jobs for carbs in my machine shop.

Straight bore ( I think in some areas it's know as rifle boring)- This gives the best top end, but midrange and low end get worse

Oval bore - definetly the best, this keeps the low end power, a slight decrease in midrange, and plenty on top.

With a straight bore you lose power on low end because you are removing material from the pilot area and get improper atomization of your flow, it shortens the diffuser lenght of your pilot. But the biggest factor is Air flow velocity is decreased and this plays a major factor in low speed atomization.

oval boring starts the oversizing around 1/4 throttle opening, so at low slide opening you still have your maximun air velocity through the carb. As the slides climb up, you have enough air velocity to atomize your fuel.

Oval boring is more expensive and requires more skill and time.


Hope this helps!
 
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