>Rochester 4GC Carburetor Repair Tips

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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.

2 Responses

  1. Information you may know:
    I was surprised to find a Carter YF-7283S on a 1961 305 cu.in. V-6 GMC
    truck. It seems a few different types of carbs were used on these motors!

    • No surprise to me. Vehicles were often produced with more than one type of carburetor and sometimes multiple carburetor numbers for the same type. Then there is the possibility of replacement carburetors, sometimes installed when the vehicle was new to correct some problem. That is why we in the business put so much emphasis on the carburetor number. We can never be sure which carburetor was on any particular application.

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