Parts you might need - link to category Stock Carburetor Parts
Before you begin to adjust the carburetor, the valves, points, and timing should be set. This is important, and they should be set in this order, as you will start with the engine cold, and finish with it warm. It’s important to set the valves, points, timing and to check the choke before setting the carburetor, as they all work together for a smooth running engine. Details regarding these settings are given in the links below.
The following descriptions apply to all types of carburetors -
There is a lever on the left side with a cable connected to the bottom of it. This is the throttle lever; the cable is the accelerator cable.
Note:Before adjusting the carburetor, it is essential that the accelerator cable be properly adjusted. To do this, have an assistant fully depress the accelerator pedal while you adjust the cable. Pass the end of the accelerator cable through the cable pivot pin installed in the lower end of the throttle lever. The books say that with the pedal fully depressed and the cable extended forward, the throttle lever should be wide open and attached to the cable such that there is about 1mm of clearance between the throttle lever and the carburetor.
You may find it easiest to simply note where the clamp goes on the cable end in this position (wide open), then let up on the pedal and make the connection with the system relaxed. Or, if working by myself, I find that I can come very close by adjusting the cable as follows: With the idle screw against the very bottom of the stepped cam, pull the cable back finger-tight and snug down the screw to secure the cable. It takes three hands — I use my channel lock pliers and hold the end of the cable to the throttle lever while I tighten the screw with the other hand.
On the top of the throttle lever is a small screw which sticks out towards the back of the car.
This is the “idle adjustment screw” on the 28 and 30 series carburetors,
and called the “fast idle adjuster” on the 30PICT/3, 34PICT/3, 31PICT and Brosol H30/31.
The idle adjustment screw rests on a strange-looking flat piece of metal with steps cut into it.
This is the fast idle cam, and works with the choke to give a reliable idle on a cold engine.
The engine must be warm to set the carburetor so that the choke is off (i.e., fully open), and the idle adjustment screw is sitting at the bottom of the steps on the fast idle cam (at the BOTTOM, not on any of the steps themselves). Directly beneath the fast idle cam on the left side of the carburetor you will see (on the older models) a single screw with a spring wrapped around it. This is the volume control screw, and this type of carburetor can be called a “one adjusting screw” type of carburetor. The later model carburetors also have a larger bypass screw that is used for setting the idle speed – the fast idle adjustment screw and stepped cam are NOT used to adjust the idle speed on these “two adjusting screw” carburetors.
On the side of the carburetor body is a barrel-shaped object, a little larger a pen-light battery, with a black wire connected to the outer end. This is the idle fuel cutoff valve (solenoid). On older model carburetors it’s on the right side, and on later models it’s on the left, close to the throttle arm. This valve shuts off the flow of fuel when you turn off the engine, to prevent “running on.” Be sure the wire is connected and that it runs to the (+) terminal on the coil. (Also attached to this terminal is the black wire that provides power to the automatic choke.) Make sure that the idle cutoff valve is screwed into the carburetor snuggly, and not rattling loose. Don’t overtighten it though, it’s got a fine brass thread and screws into aluminum — both relatively soft metals.
Note: You can test the operation of the idle cutoff valve solenoid very easily. Turn on the ignition (don’t start the car), and pull off the wire on the solenoid. Touch the wire back onto the connector, and you should hear a clicking sound as the valve inside moves. If you do not hear a clicking sound, check to make sure there is power (12 volts) to the wire (small trouble light, voltmeter, etc.). Replace the solenoid if necessary. If it’s not working, you won’t get a proper idle, and you’ll get rough running at traffic speeds, too.
As stated previously, before attempting to adjust the carburetor make sure your engine is warm and the choke butterfly standing upright. Make sure the air cleaner is seated firmly on the top of the carburetor before beginning the adjustment — the engine expects it to be there.
The 28PCI, 28 PICT, 28PICT/1, 30PICT/1, and 30PICT/2 all have one adjusting screw in the left side of the carburetor (the Volume screw) and an idle speed screw on the throttle arm. They can all be tuned using our procedure for the Adjustment of “Single-Screw” Carburetors.
The 30PICT/3, 31PICT, H30/31 and 34PICT/3 all have two adjusting screws in the left side (the smaller Volume and larger Bypass screws) and a fast-idle screw on the throttle arm.
They can be set using the our procedure for the Adjustment of “Two-Screw” Carburetors.