BASIC CARBURETION

      The automotive carburetor, although relatively inexpensive and easy to service, is expected to meet many demands of the car owner, such as:

1. Maximum Power
2. Economical Operation throttle maneuvers or weather conditions
3. Flexibility (e.g. altitude)
4. Smooth operation regardless of
5. Rapid Acceleration

A - O" HG VACUUM NO VELOCITY   B - 1" HO VACUUM LOW VELOCITY LAROE AREA   C - 1" HO VACUUM HIGH VELOCITY SMALL AREA   D - 2" HO VACUUM MODERATE VELOCITY MODERATE AREA

      When the engine piston moves down, it creates suction in the intake manifold. Assuming that there is suction at the bottom of this pipe and atmospheric pressure at the top, air will flow through. As shown in the mercury U-tubes, the greatest suction is at the point of smallest area or highest velocity (C). Note in (E) that if the tube points into the air stream it merely transmits the pressure in the pipe to the mercury in the U-tube. We use these principles to draw fuel from a carburetor.

      This is a simple single jet carburetor. The float mechanism maintains the fuel level in the carburetor bowl. We know that by placing one venturi inside another we can increase suction (F,G). The main discharge nozzle is located at the smallest area or point of greatest suction. As the piston speed increases and suction increases, fuel is drawn from the float bowl up through the main discharge nozzle and enters the main air stream. When the piston stops there is no suction and the fuel level drops below the tip of the nozzle, thus preventing leakage. Note that the balance tube faces directly into the air stream, and so transmits pressure to the fuel in the float bowl.
      The difference in pressure between the balance tube and main discharge nozzle causes fuel flow.