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Rochester 4GC Rebuild Questions

Guest dstaton

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Guest dstaton

I am reassembling my carb for my '62 Starfire with a kit from Mike's Carburetor Parts. My carb is the original Rochester 4GC, part number 7020950.

My car has had A/C dealer-added. The Oldsmobile dealer instructions don't mention changing carbs, but I read elsewhere that an A/C 4GC had a different Rochester part number. How would this carb differ from the A/C equipment, carb number 7020951?

Also, I need some clarification as I reassemble.

1 Power Piston Assembly

I was unable to remove it and my kit didn't have the replacement part. Issues?

2 Primary Float Balance Spring

Which side of the tang, in or out?

3 Accelerator Pump Inlet Strainer

The screen only fit if I domed it and it is held into place by the resultant tension. I found no retainer upon disassembly.

4 Accelerator Pump with Leather

My kit only had a rubber replacement for the leather. The shaft is to be reused. Can't get the leather off without destroying it. Can the leather be reused? Should it receive some oil, or something..? It creates pressure when in place. (see Photo 7)

5 Idle Compensator System

I can find no attachment points for this part on my carb, nor did one come off.

6 Secondary Float Settings

Specs indicate the toe should be flush with the metal surface of the airhorn assembly. The metal tang for which there is a corresponding slit in the gasket forbids the floats from falling further than this shot shows.

7 Accelerator Pump Spring

Should I adjust the spring over lap to increase the diameter, and compression?

Wow, I'm gonna owe someone a beer.










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Wow, I'm gonna owe someone a beer.



Generally, the company selling the kit would be the place to ask questions, however:

(1) Power piston is "staked". Removal can generally be done by exerting EVEN pressure on the piston. If you don't want to remove it, check to make certain it moves up and down without binding.

(2) From memory, the float balance spring is on the secondary, not the primary, and should be installed such that it helps lift the float.

(3) Screen under pump is held in by either a retaining ring or the return spring. Screen in bowl is held by three projections on casting.

(4) DO NOT DESTROY THE LEATHER!!!!!!! Soak in light machine oil for a couple of hours, and reuse the leather pump!

(5) Many of the A/C carbs and A/T carbs had hot idle compensators. Manual transmission carbs generally do not.

(6) No comment other than if you have the correct tagged carburetor, and received the correct gasket, this should not be an issue.

(7) Sorry, do not understand this question.


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Guest dstaton


Thanks for the reply. I think I got it now.

Do I understand correctly that the hot idle compensator cannot be added to my 7020950 because my bowl assembly doesn't have the journal taps to receive it?

About photo 7, I was wondering if the spring supporting the leather could be increased in diameter by overlapping it by fewer coils, causing it to exert more pressure on the leather to improve the seal, assuming that the leather has degraded and shrunk over the years.

I love the fact that my car has a leather part in the engine.


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