Automotive Carburetion Made Easy



BASIC CARBURETION Continued

PUMP PISTON MOVES DOWN AS THROTTLE IS OPENED		Note that in the idle range the ac-celerator pump is fully charged with fuel. When the throttle is suddenly de-pressed, air flow increases instantly. Fuel, being heavier than air, lags behind somewhat. To prevent hesittaionduring this lean period the carburetor uses an accelerator pump connected directly to the throttle. As the throttle is depressed, this pump instantly sprays a charge of fuel into the air stream, thus pre-venting leanness. As shown in the illustration, the pump also compenpensates for a possible lag in the transfer range, when idle fuel stops and main nozzle fuel starts.

The automatic choke regulates the mixture for proper cold weather operation. The coil is bimetallic and expands or contracts with changes in temperature. As it cools it closes the choke valve, thus reducing air flow. Heat from the exhaust manifold gradually relaxes the coil tension, thus permitting the valve to	open as the engine warms up. Since the automatic choke is linked to the fast idle mechanism, it also regulates the throttle position during cold starting and engine warm-up. Always depress accelerator once before starting during cold weather to as-sure proper operation of choke mechanism.

CHOKE VALVE

FROM EXHAUST MANIFOLD STOVE

Fuel vaporization may seriously disrupt carburetor operation under hot weather conditions, particularly at idling speeds. Wherever advantageous, atmospheric vents	are used, thus allowing these vapors to escape from the carburetor bowl instead of passing through the carburetor metering channels.

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