6. IDLE SPEED AND MIXTURE

Function

The idle circuit is contained in the first stage of the carburetor. Fuel is drawn up into a cavity within the carburetor cover through the idle fuel jet. Here it is mixed into an emulsion with the air entering through the idle air bore. By way of a channel, this emulsion flows to the fuel mixture outlet at the idle mixture screw and to the by-pass bores. The by-pass bores serve to improve transition from idle jet to main jet system when opening the throttle.

IMPORTANT

The carburetors must be synchronized in order to prevent the possibility of performance problems.

Adjustment

1. With car at full operating temperature, synchronize the throttle plates of each carburetor using "Syncro-Test" device and adapter piece. Adjust to specified idle RPM. (See Fig. 1)

2. Adjust idle mixture screws to the same position by blocking off the idle air bore in the top cover, one at a time, and matching the RPM drop. This procedure prevents damaging the idle mixture screws. (See Fig. 2 and 2A)

3. Observing tachometer and exhaust analyzer, adjust throttle valves, and mixture as necessary to arrive at specified idle RPM and specified carbon monoxide. (See Fig. 3)

NOTE: Continually check balance of throttle valves (using "Synchro-Test") and mixture (using idle air bores) as the adjustments are made.