Carburetor Idle RPM and Idle Air Mixture Adjustment

Carburetor Idle RPM and Idle Air Mixture Adjustment

1. There are two external carburetor adjustments, and they affect only the idle performance. They are the idle RPM and idle air mixture adjustments
2. Turn Gas Valve under dash on passenger side to open (Pointing down)
3. Preparation: Fully warm the engine up, move spark control (on left side of steering wheel) up, turn the under dash choke control knob full clockwise and then counter clockwise about one turn, and move the hand throttle lever (on the right side of the steering wheel) all the way up. If engine tend to die, pull the throttle lever down a little.
4. Preliminary Idle RPM adjustment: Turn the adjusting screw on the carburetor throttle arm until the end of the threads is making contact with the stop. You should now be able to put the hand throttle lever all the way up without the engine tending to die. Go back to the adjusting screw on the carburetor throttle arm and adjust it to a low RPM, just faster than where engine tends to stall. This will ensure that the carburetor idle circuit if functioning.
5. Idle Air mixture adjustment: Slowly turn the idle air mixture screw clockwise until the engine begins to stall, and note the position. Slowly turn the idle air mixture screw counter clockwise until the engine begins to stall and note the position. Now, adjust the screw about half way between the two positions, and you will often hear a very slight increase in engine RPM. (Idle air mixture screw should be about 1–1/2 turns out from full clockwise.)
6. Final Idle RPM adjustment: Pull the spark lever about 3/4 down. Readjust the idle RPM adjustment for the idle speed that you prefer. (If adjusted too high, you will likely tend to grind gears when driving.)

Source: http://www.model-a.org/procedures_full.html