>Rochester 4GC Carburetor Repair Tips


Correct Throttle Body Gasket

Installing the wrong gasket on a 4GC throttle body can make the carburetor act like it has a vacuum leak. It might run ok at higher RPM, but it will not idle properly, if at all.

Assuming your carburetor was running ok at one time, it would be safe to assume it has the correct gasket. Match it with the gasket from your carburetor kit.
Accelerator Pump
There were a multitude of different accelerator pumps used on the 4GC carburetor. Hopefully you bought your kit, or will buy your carburetor kit using the carburetor number as a cross reference, not by going by the application. Still, you should be careful that you install the correct pump.

A pump that is too big in circumferance will bind and not allow the throttle to return to idle. A pump too small in circumferance will cause the carburetor to hesitate.

Make sure your accelerator pump return spring is returning the accelerator pump to it’s idle position.

Checking the Throttle Body
Did you remove the throttle plates? If so, then check for excessive gaps around the plates. Switching the plates, or turning them over could result in too much gap. Too much gap will make the carburetor hard to adjust for the idle speed. It may not idle down at all. This would be the same as stepping on the accelerator a little bit.

>Carburetor Problems?

>Carburetor Is Flooding

These are the most likely causes.

The needle and seat is not closing. Most likely there is dirt causing it to stick open, but the needle could also be defective.

The float level is incorrect.

Gas is getting inside the float making it heavier than normal.

Carburetor unloading isn’t correct. Depress the throttle all the way. The choke plate should be opening.

To eliminate the above causes, the carburetor should be rebuilt.

The Engine Hesitates When Accelerating.

Most likely the accelerator pump is defective, or the delivery circuit is plugged.

Rebuild the carburetor.

Engine Surges

Fuel restriction. Check the lines for bends and kinks. Replace any badly worn hose.

Dirt, or water in the fuel. Clean out the gas tank and change the fuel filters.

Main jets may the the wrong size. This would be due to someone changing them recently.

Vacuum leak. Check the carburetor throttle to make sure it isn’t loose in the throttle body. Might be a leak at the intake manifold, or perhaps where the carburetor mounts to the manifold.

Fuel level is too high, or too low. Check the float level.

Choke Problems

When the choke isn’t opening like it should:

For the thermostatic type of choke with the metal coil – heat up some water and place the choke in the water. It should look like it’s unwinding. If it doesn’t, then replace the choke.

Electric choke – Simply hook up the two leads to the choke to a 12 volt source. The choke should open fairly quickly.

Some models have the choke mounted in the manifold. The heat from the manifold heats up the coil making the choke open. Assuming you have already tested the choke in hot water and it works fine, but doesn’t work when on the car, then chances are the manifold isn’t heating up the choke. This is probably due to the manifold being clogged around the choke area.