Correct L48, 350 Carb Base Gaskets - Team Camaro Tech
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post #1 of 19 (permalink) Old Sep 10th, 19, 04:50 PM Thread Starter
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Correct L48, 350 Carb Base Gaskets

I'm rebuilding a 69 L48, 350 engine to mostly stock condition. Can someone tell me what the correct Quadrajet base gasket should be? It looks like there is a paper gasket and a metal heat shield gasket. Should there be a third gasket between the carb and metal heat shield gasket? This looks like a vacuum leak for sure. Any info would be helpful.
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post #2 of 19 (permalink) Old Sep 10th, 19, 05:22 PM
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Re: Correct L48, 350 Carb Base Gaskets

I had to figure this out once before. Itís just the two gaskets. The metal one is a show stopper if you donít have it. IIRC the metal goes on first and then the paper gasket. No third one needed, the metal one is really thin.

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post #3 of 19 (permalink) Old Sep 10th, 19, 05:40 PM Thread Starter
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Re: Correct L48, 350 Carb Base Gaskets

So you are saying the paper or felt material goes on the intake (because it has the cutout for the EGR). Then the thin metal gasket goes between the felt material and the carb? That is the way it came apart. It would seem to me there should be another felt gasket between the thin metal gasket and the carb to keep vacuum from leaking.
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post #4 of 19 (permalink) Old Sep 10th, 19, 05:47 PM
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Re: Correct L48, 350 Carb Base Gaskets

No, other way around. Metal goes down first to block the heat riser.

Letís see if someone else chimes in, itís been a few years since Iíve had the carb off. Iíll see if I can tell without taking the carb off.

But, no third gasket.

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post #5 of 19 (permalink) Old Sep 10th, 19, 06:01 PM
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Re: Correct L48, 350 Carb Base Gaskets

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Originally Posted by 69L48Z27 View Post
No, other way around. Metal goes down first to block the heat riser.

Letís see if someone else chimes in, itís been a few years since Iíve had the carb off. Iíll see if I can tell without taking the carb off.

But, no third gasket.

My first 69 was an L48 back in '75, When I rebuilt the carb I neglected to install the thin, stainless I believe it is, metal shield, and had issues within a few days. The gasket was getting burnt up. Was actually wondering why it was laying on my work bench until the local speed shop said what it was for.


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post #6 of 19 (permalink) Old Sep 10th, 19, 06:03 PM
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Re: Correct L48, 350 Carb Base Gaskets

Looks like I have my info wrong. It looks like the metal gasket is against the carb.

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post #7 of 19 (permalink) Old Sep 10th, 19, 06:04 PM
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Re: Correct L48, 350 Carb Base Gaskets

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Originally Posted by 69Z28 View Post
My first 69 was an L48 back in '75, When I rebuilt the carb I neglected to install the thin, stainless I believe it is, metal shield, and had issues within a few days. The gasket was getting burnt up. Was actually wondering why it was laying on my work bench until the local speed shop said what it was for.
Yep, that how I figured it out. My ran bad from the get go. Put the metal gasket in and just like that it was fixed.

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post #8 of 19 (permalink) Old Sep 10th, 19, 06:38 PM
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Re: Correct L48, 350 Carb Base Gaskets

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Originally Posted by 69L48Z27 View Post
Yep, that how I figured it out. My ran bad from the get go. Put the metal gasket in and just like that it was fixed.



After reading your MISINFO comment, I was wondering about the configuration since this happened in 1975...loosing memory these days. Now I'm not sure. I believe the metal shield laid on the intake, to shield the gasket from the channels cut into the intake surface and the exhaust heat that is there, and then the gasket and then the carb.


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post #9 of 19 (permalink) Old Sep 10th, 19, 06:43 PM
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Re: Correct L48, 350 Carb Base Gaskets

Thatís what I thought too. I just went out in the garage and it looks like the metal is on top against the carb on mine right now. Car has been running great since 2012 with it this way.

I know I had to figure out where the heat shield went at some point. There was little to no info anywhere on the web about which one went on the top or bottom.

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post #10 of 19 (permalink) Old Sep 10th, 19, 07:14 PM
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Re: Correct L48, 350 Carb Base Gaskets

Quote:
Originally Posted by 69L48Z27 View Post
Thatís what I thought too. I just went out in the garage and it looks like the metal is on top against the carb on mine right now. Car has been running great since 2012 with it this way.

I know I had to figure out where the heat shield went at some point. There was little to no info anywhere on the web about which one went on the top or bottom.

I have an LM1 69 Impala Custom with 45000 original (little old lady, really) miles to check against, but it's not where I am now to do so. I'm sure there is someone here on T.C. that knows the correct set up.


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post #11 of 19 (permalink) Old Sep 10th, 19, 07:19 PM
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Re: Correct L48, 350 Carb Base Gaskets

Quote:
Originally Posted by 69L48Z27 View Post
Thatís what I thought too. I just went out in the garage and it looks like the metal is on top against the carb on mine right now. Car has been running great since 2012 with it this way.

I know I had to figure out where the heat shield went at some point. There was little to no info anywhere on the web about which one went on the top or bottom.

Garth, you're more than likely more correct than I am. I've owned a few Pontiacs as well, 69 Judge RAIII had a Rochester, but I've seen a totally different base gasket on them.


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post #12 of 19 (permalink) Old Sep 10th, 19, 07:28 PM
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Re: Correct L48, 350 Carb Base Gaskets

Here is an older post from the Corvette Forum explaining the need and usage on the hot slot
design intakes. I've also seen where John Z states the same info.
https://www.corvetteforum.com/forums...d-problem.html
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post #13 of 19 (permalink) Old Sep 11th, 19, 03:19 AM Thread Starter
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Re: Correct L48, 350 Carb Base Gaskets

Thanks alanjs. That thread pretty much explained and answered my concern. Since my manifold is already on the engine, I'll be looking for that third gasket for mine.
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post #14 of 19 (permalink) Old Sep 11th, 19, 04:31 AM
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Re: Correct L48, 350 Carb Base Gaskets

The Corvette post is always how I used the metal plate, sandwiched between two fiber gaskets. I also plugged my heat riser holes at the carb to further reduce heat. Ethanol fuel evaporates fast enough now, without the added heat
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post #15 of 19 (permalink) Old Sep 11th, 19, 06:11 AM
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Re: Correct L48, 350 Carb Base Gaskets

The Corvette link is how I did mine on my '68 350.

The gaskets came in the Weber Q-Jet re-build kit with a few more gaskets thrown in with different thicknesses. No SS shield was in the kit. I re-used the one that came with the stock Q-Jet and L48 manifold.

I made the "Stainless steel heat shield sandwich" using the heat retardant (asbestos? has the smile cut out) gasket first directly on the manifold. Then the thin stainless metal heat shield, then one of the supplied gaskets. I used the medium thickness.

Engine has been running great for over five years.

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