VCCA Home Forums GENERAL DISCUSSION New User Forum Setting Idle on 1948 Chevy Truck

My 48 Chevy truck idles very fast and almost diesels when I turn it off. Is there any trick to setting the idle other than turning the idle screw until I get the speed that seems right. I don't have any instruments except my ears and eyes.

You can use a tachometer to set the idle speed if you have one. Otherwise set it by how it idles and accelerates off from idle. Yes turning the throttle adjusting and idle mixture screws are the way to get it to run its best.

The rod that connects the throttle arm to the accellerator pump plunger maybe sticking causing the throttle to not close properly, Otherwise the screw near the throttle arm should adjust idle speed. This screw may have been turned in to compensate for a bad idle speed mixture which is adjusted by the other screw on the base of the carb.
Tony

ASSUMING that the engine and carburetor are in good shape, try the following:

Start the engine
Run at fast idle until engine is at operating temperature
Turn off engine
Turn the idle mixture screw (brass screw with spring all the way clockwise until "finger tight" COUNTING THE NUMBER OF TURNS (can reverse process if you wish)
Turn the idle mixture screw counterclockwise 1 full turn (360 degrees) with real gasoline, 1 1/4 turn with ethanol-diluted gasoline.
Start the engine
Using the throttle positioner screw, adjust the idle RPM (clockwise higher RPM, counter-clockwise lower RPM)
Once you are happy with the RPM, disconnect the throttle rod from the carburetor. If no change in RPM, you are done.
If RPM changes with the step above, remove the carpet from under the footfeed or determine where throttle rod might be sticking.

Note that with the idle set as above, it may be necessary to use some amount of choke after starting a cold engine, until the engine obtains operating temperature.

Jon.

Thanks for this procedure Jon. I will use it on both of my vehicles.