The velocity of fuel, and mixture, thru a carb is dependent on the pressure drop between atmosphere (air box) and the inside of your engine. If you make this pressure drop bigger it sucks fuel harder. 2 ways, increase the pressure outside (pressurise the air box) or lower the pressure inside the engine by making more space for fresh mixture (by which I mean get rid of the old mixture) to get in, make it easier for it to get in and make the piston move faster. Too large a crank case volume and you just cant fill it, and that alters the pressure drop.
Small carbs hit their max flow rate at a slower rate, they are therefore working at their best over a greater range of engine speeds. As with the basin taps once it's flowing at it's max it can't flow any faster, it's a 28mm bore hole
Big carbs only hit their max flow rate at a higher rate, they are only working efficiently at a very high engine speed, you can suck more air thru a 35mm hole, but you need a much bigger pressure drop to do it properly.
You can lengthen or shorten the inlet tract to help with the pressure drop
Max driveability long inlet tract small carb, flattest power curve, probably more torque over a wider rev range
Max power big carb short inlet tract, but it won't have a wide power band
But it's not just about putting big carbs on, you have to adjust everything else to let them work. You could write a book about carb tuning. Ask Eric Gorr
http://www.chicagostories.net/ericgorr/ ... uning.html
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