1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!!

[Scott K.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

any ideas as to how to get a good seal from the carb to the intake manifold? I have tried new gaskets, torquing the bolts in the proper sequence and i still have a leak on the passenger side right next to where the choke assembly is, this is obviously causing me drivability issues and issues with the vacuum operated items like the wiper door and headlights.

Is this what your set-up looks like?
(this is my 72, stock.)

[Mark E.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

Nice photo showing thickness of the gasket. What this doesn't show is the shape of the inside openings of the base gasket, which is also important.

[Scott K.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

Nice photo showing thickness of the gasket. What this doesn't show is the shape of the inside openings of the base gasket, which is also important.

yeah well.. I'm a helpful kinda guy -- but not pulling the carb off to show a picture. That pic is all there is . If you have a pic of the inside as you suggested, then post away :-)

[Joe L.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

All------


This is what it looks like:

[Mark E.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

All------

This is what it looks like:

Nice shot. Your vintage Q-Jet uses a gasket with an open center (not three or four separate holes), with material shaped like the one pictured between the two primary bores (this shape is critical since it allows/blocks a vacuum signal to the base plate), no slots around the primary bores (important for same reason), and no exhaust cross-over slot between the two front bolt holes.

Of course, none of these details will cause an external vacuum leak like you're seeing, but are important for proper operation.

[Christopher R.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

in looking at both picture the carb picture shows a thin gasket while the bottom is much thicker. is the thin version the way to go or do the emission cars take the thicker version. I will take some pictures today of mine and post

[Mark E.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

in looking at both picture the carb picture shows a thin gasket while the bottom is much thicker. is the thin version the way to go or do the emission cars take the thicker version. I will take some pictures today of mine and post

As Joe stated earlier, OE is a thick insulating gasket. Scott's and Joe's photos show what this looks like.

[Christopher R.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

ok, i found the proper gasket exactly like the one you have pictured. Two questions. Do we use just the insulator or the thin gasket above and below the insulator. What is your rule of thumb for tightening the four bolts. i have the assembly manual and it says to use 168 inches of torque to the bolts but I don't want to be that guy as you said that is over tightening them!!!

Thanks.

[Joe L.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

ok, i found the proper gasket exactly like the one you have pictured. Two questions. Do we use just the insulator or the thin gasket above and below the insulator. What is your rule of thumb for tightening the four bolts. i have the assembly manual and it says to use 168 inches of torque to the bolts but I don't want to be that guy as you said that is over tightening them!!!

Thanks.

christopher-------


No gaskets are used in conjunction with the thick insulator. The insulator serves as both a gasket and an insulator. By the way, I do not recommend that these insulators be re-used, even once. These are a "compression-seal" type of gasket and they have compression-limiting inserts at the bolt holes. So, once they are compressed, subsequent "re-compression" is not possible.

168 inch/pounds of torque is equal to 14 foot/pounds. That is not excessive torque for these bolts and I'd use just what the AIM specifies.

Note: if one wishes to re-use a previously installed insulator, then I would recommend that thin carb flange gaskets be installed on either side of the insulator. That might slightly alter the choke rod adjustment but it would likely be necessary to achieve a good seal. In fact, that may be why folks find these gaskets used in conjunction with the insulator. GM didn't do it that way and I'd never do it that way, but if one wants to "cheap-out", that's what I'd recommend.

[Scott K.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

christopher-------


No gaskets are used in conjunction with the thick insulator. The insulator serves as both a gasket and an insulator. By the way, I do not recommend that these insulators be re-used, even once. These are a "compression-seal" type of gasket and they have compression-limiting inserts at the bolt holes. So, once they are compressed, subsequent "re-compression" is not possible.

168 inch/pounds of torque is equal to 14 foot/pounds. That is not excessive torque for these bolts and I'd use just what the AIM specifies.

Note: if one wishes to re-use a previously installed insulator, then I would recommend that thin carb flange gaskets be installed on either side of the insulator. That might slightly alter the choke rod adjustment but it would likely be necessary to achieve a good seal. In fact, that may be why folks find these gaskets used in conjunction with the insulator. GM didn't do it that way and I'd never do it that way, but if one wants to "cheap-out", that's what I'd recommend.

To answer the question you asked, the thick gasket should be new, never used prior and is not used in conjunction with another gasket. That thinner brown gasket you see in the picture is just under the carb; then there's the silver piece AND THEN the subject thick gasket.

does that help?.

[Joe L.]

Re: 1972 Corvette Carb to Intake seal - Just cannot get rid of this last vacuum leak!

To answer the question you asked, the thick gasket should be new, never used prior and is not used in conjunction with another gasket. That thinner brown gasket you see in the picture is just under the carb; then there's the silver piece AND THEN the subject thick gasket.

does that help?.

Scott------


The "thinner brown gasket" is NOT the carburetor base gasket. The "thinner brown gasket" is part of the carburetor assembly and is located between the carburetor float bowl (the "gold" colored part) and the throttle body assembly (what I assume you call the "silver piece"). Of course, that gasket could be leaking. However, to replace it you need to partially disassemble the carburetor. That gasket was never available from GM as a separate part but only as part of a rebuild kit (which is no longer available from GM). It may or may not be available in the aftermarket separately. Generally, if one gets into a carburetor that far, one uses a kit and rebuilds the entire carburetor.

The insulator gasket mounts between the carburetor throttle body and the intake manifold. The thin gaskets I described in my last paragraph would be used on either side of that insulator to improve sealing IF one were to re-use an insulator which I do not recommend. This would be sort of a "bubba" type of repair.