CARBURETION THEORY

CHAPTER l

    To efficiently service a carburetor, a mechanic should have some knowledge of the purpose of the carburetor and how it works. This chapter is a general review of carburetion theory which will apply to all models of Holley carburetors. The following chapters covering each carburetor model include a section which explains how the basic theory applies to the model concerned.

1.     PURPOSE OF THE CARBURETOR

    The carburetor delivers a combustible mixture of fuel and air to the intake manifold of the engine. It automatically controls the amount of fuel being mixed with the air to meet changing engine operating conditions, delivering a greater amount of fuel when high power output is required and less fuel for economical cruising.

2.     THE ENGINE

   The effect of the engine upon the carburetor may be compared with that of a

suction pump. As each piston moves downward on its intake stroke, a partial vacuum is created in the cylinder. This draws the fuel-air mixture from the carburetor and intake manifold into the cylinder through the opened intake valve. (Figure 1.)

    If an engine was intended to run at only one speed and load, its carburetor could consist of a simple nozzle spraying fuel from a gravity

feed tank into the intake manifold. (Figure 2.) Once the rate of flow of the fuel was adjusted to give a satisfactory mixture, no change would be necessary.