Your application is a bit unclear but as a very rough guide, determine the maximum piston velocity or at least the crankpin linear speed in feet per second or some similar units.
Using this speed and the area of the piston find out how much air the engine tries to suck in on the down stroke at max piston velocity.
Using that volume of air per second find a carburetor with a venturi that will pass a similar volume of air at a speed below the speed of sound. How much below? Say 85% for a utility engine and maybe only 50% for a race engine.
Your question did not define any parameters on which you wish to base your selection.
Are you looking for cheap parts for a lawn mower for instance.
Are you looking for a carby for a particular class in racing.
What rpm range.
Does it need to operate at large angles, say like in a brush cutter or chain saw.
Is it 2 or 4 stroke.
I was attempting to highlight that lack of the required data is making it impossible for us to help you by selecting a property that might influence selection of fashion accessories, but probably not the selection of a carburetor, unless you consider a carburetor a fashion accessory.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.