27 February 2018

Carburetor size

The size of a carburettor is generally given in terms of the diameter of the venturi tube in mm and the jet size in hundredths of a millimetre. 

The calibrated jets have a stamped number which gives the flow in ml/min under ahead of 500 mm of pure benzol. 

Jet size is usually one-sixteenth of venturi size. 

For a venturi of 30 to 35 mm size, the pressure difference (p1-p2) is about 50 mm of Hg. The velocity at the throat is about 90 - 100 m/s and the coefficient of discharge for venturi Cda is usually 0.85. 

Normally the size of carburettor 1 or 2, 3 or 4 barrel, a little bit of confuse about the size so there is a formula for choosing a proper size in cfm for your engine.

Formula :

First step: CC full form is cubic displacement divided by 2.

Second step: Maximum RPM is divided by 1728.

Third step: Multiple above two step figure. 

Fourth step: Multiply third step answer with volumetric efficiency for that engine depending on what you have done with your heads and exhaust. 

Fifth step: Final Answer in cfm.