1972 LT-1 Carburetor

[Ron E.]

Recently purchased a '72 LT-1 and the carburetor accelerator pump appears to be leaking. Would anybody happen to have the correct diaphragm p/n as well as the carb/intake gasket p/n?

I have never removed a carburetor before and am somewhat apprehensive about removing linkages, etc. Any tips on how to go about removing the fuel line, carb, etc? Do I remove the fuel line fittings at the carb or leave the hard line connections and remove at the front of the engine? What is the correct torque when reinstalling the carb?

Thanks for the help!

Ron

[Joe L.]

Re: 1972 LT-1 Carburetor

Recently purchased a '72 LT-1 and the carburetor accelerator pump appears to be leaking. Would anybody happen to have the correct diaphragm p/n as well as the carb/intake gasket p/n?

I have never removed a carburetor before and am somewhat apprehensive about removing linkages, etc. Any tips on how to go about removing the fuel line, carb, etc? Do I remove the fuel line fittings at the carb or leave the hard line connections and remove at the front of the engine? What is the correct torque when reinstalling the carb?

Thanks for the help!

Ron

Ron------


The GM part number for the diaphragm was GM #2414214 but it's long-since GM discontinued. For this part I would not use NOS even if you could find one. You're much better off with a current Holley part (which likely will include ethanol-resistant material). I believe the Holley part number is either 8-103 or 8-153. A complete rebuild kit which includes this part is Holley #37-1539.

The carb base gasket was GM #3999259 but it's long-since GM-discontinued. Reproductions or replacements should be available, though. Dr. Rebuild is a great source for these.

[Ron E.]

Re: 1972 LT-1 Carburetor

Joe -

Holley indicated that their p/n 135-3 is the correct replacement. Here is a link to the diaphragm at Summit Racing's web site:

https://www.summitracing.com/parts/hly-135-3

Does this appear to be correct?

Thanks,

Ron

[Joe L.]

Re: 1972 LT-1 Carburetor

Joe -

Holley indicated that their p/n 135-3 is the correct replacement. Here is a link to the diaphragm at Summit Racing's web site:

https://www.summitracing.com/parts/hly-135-3

Does this appear to be correct?

Thanks,

Ron

Ron------


This is the diaphragm for the vacuum secondaries, not the accelerator pump.

The numbers I provided might be old Holley numbers and may have been superceded by now. However, I would think that Holley could use them to find the current part number.

[Ron E.]

Re: 1972 LT-1 Carburetor

Joe -

As I mentioned, I am not familiar with carburetors...mine is leaking from the front of the carb on the driver's side. Is this the vacuum secondary or accelerator pump?

[Dan A.]

Re: 1972 LT-1 Carburetor

It wouldn't have anything to do with the vacuum secondary system. Have you tried gently tightening the bowl screws? It's not uncommon for them to back out a little. It could also have something to do with the primary inlet fitting.

[Ron E.]

Re: 1972 LT-1 Carburetor

Holley was able to provide the correct diaphragm p/n (135-5 for the "old style" and 135-10 for the GFLT material that is resistant to ethanol). The leak is definitely coming from the accelerator pump. The prior owner used ethanol based fuel and I am sure it deteriorated the diaphragm.

[Joe L.]

Re: 1972 LT-1 Carburetor

Holley was able to provide the correct diaphragm p/n (135-5 for the "old style" and 135-10 for the GFLT material that is resistant to ethanol). The leak is definitely coming from the accelerator pump. The prior owner used ethanol based fuel and I am sure it deteriorated the diaphragm.

Ron------


There could very well be problems with other gaskets and seals in the carburetor. I think the best plan would be to rebuild the carburetor with a kit which contains parts rated for ethanol blended gasoline.

If you intend to drive the car, you have to be prepared these days for ethanol fuel. It's quite common (in California it's extremely hard to avoid and that may also be true in other states). When you're out on the road and you need fuel, you've got to use what's available where you're at.

[Jim T.]

Re: 1972 LT-1 Carburetor

I have bought Holley individual parts at Orielly's for my Holley's including accelerator pump parts. I use pump gas.

[Jerome P.]

Re: 1972 LT-1 Carburetor

I had the same problem with a leaky accelerator pump gasket. I disconnected the fuel lines at the carb.