Carburetor: Description and Operation

Fig. 1 Exploded view of Hitachi DCH/DFP 340 carburetor (Part 1 of 2):

Fig. 1 Exploded view of Hitachi DCH/DFP 340 carburetor (Part 2 of 2):

This carburetor, Fig. 1, is a two barrel, downdraft type unit comprised of a low speed or primary side, and a high speed or secondary side, both integrated into a single unit.
An electric choke is used and incorporates a thermostatic spring which automatically works in response to changes in ambient temperatures, controlling the choke valve and facilitating easier starts. The choke valve is positioned by the action of the thermostatic spring which is activated when the accelerator pedal is depressed. When the engine starts, manifold vacuum is applied to the choke breaker diaphragm unit. The diaphragm unit contains two springs, one of which offsets bi-metal spring tension, balancing the opening of the choke valve with tension of the bi-metal. The bi-metal spring senses engine and ambient temperatures, thereby varying the choke opening and allowing a slightly richer or leaner mixture depending on the temperatures previously mentioned.