The choke circuit is the component that helps regulate the air-fuel mixture by controlling the amount of air entering the carburetor. The choke circuit is responsible for enriching the mixture during cold starts, allowing the engine to run smoothly until it reaches operating temperature. This ensures proper fuel combustion and prevents stalling or rough idling.
The Carter BBD usually includes the choke thermostat and usually a choke pull-off is a 2 barrel carburetor which generally uses a divorced choke type of thermostat. This means the choke thermostat is mounted in the intake manifold and is connected to the carburetor choke valve by a choke rod.
When the engine is cold, the choke valve should be closed. You may have to open the throttle a bit so that it can close. The fast idle cam may be holding it.
As the engine gets hot, the thermostat will gradually open the choke valve.
A lot of the Carter BBD carburetors will have a choke pull-off attached to the carburetor. This is used to open the choke valve slightly when the engine is cold and you want to quickly accelerate. At idle the choke pull-off piston is pulled back by vacuum. As you stomp on the gas pedal, the vacuum drops allowing the piston to move out and when far enough will open the choke valve slightly (when cold), letting in some air. This is so that the carburetor doesn't flood out when cold.
Watch the choke valve. When cold it should be closed. When hot, it should be fully opened. Again, you may have to move the throttle slightly in case the fast idle cam is holding the choke.
This is the fast idle cam on the early BBD carburetor. When the engine is cold and the choke is closed, the fast idle cam moves so that the high step is on the idle screw. This increases the RPM so that the engine doesn't choke out. As the choke warms up, the lever moves to smaller and smaller points. To adjust - Adjust the warm idle 1st, then put the fast idle cam on the high step and adjust the idle screw to the RPM recommended for your engine.
Hold throttle valves wide open
Close choke valve as far as possible without forcing
Clearance (C) between top edge of choke valve and inner wall of air horn should be as listed on carb spec sheet.
Adjust by bending unloader finger on fast idle arm.
CHOKE UNLOADER ADJUSTMENT (WIDE OPEN KICK)
1978 All models
Loosen mounting post lock nut and turn mounting post with screwdriver until index mark on disc is positioned as listed in your spec chart. Hold in this position with screwdriver and lock nut.
After adjustment is completed and coil housin, rod, and carburetor are installed on engine, lift cover disc and open and close choke valve manually to see if connector rod clears sides of hole in housing cover without binding.
If rod does not clear housing cover without binding, replace with a new unit since connecting rod cannot be bent without affecting calibration.
