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1958 Buick Carter AFB -- Correct Gaskets?


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Do any of you '58 experts know what the correct gasket arrangement is for the Carter AFB 4-barrel carb? Today I pulled off the manifold of my Roadmaster a clean, used, but not rebuilt AFB I installed back in 2014. This carb started, idled and ran well at speed, but of recent had developed a bad flat spot coming off idle. I decided to swap the carb for an identical, professionally rebuilt unit I 've had on the shelf since last year. The issue I confronted halfway through the swap has to do with gaskets. On the car (probably since I bought it) was a sandwich of the gasket shown below (note the cutout for the exhaust passage) on the manifold side and a thin stainless shim on the carb side. This shim has no cutout for the exhaust passage, hence that feature would not work. (Frankly carb icing is not a concern for me.) I opted to drop the metal shim and just use the pictured gasket. (Note: the gasket that came with the rebuilt carb was a plain paper item, pictured below, that also would have blocked the exhaust passage.)

 

I finished installing the rebuilt carb and started the car. It runs well at higher rpms with steady 17 inches vacuum. It runs unevenly at idle and vacuum is unsteady around 13 inches. I suspect a gasket leak, and will run some checks for that tomorrow. The question is, what gasket or gaskets/shims did Buick use? If that information is in the Shop Manual, I can't find it. Likewise zero info in the big parts books. I did find in my 1959 Cadillac Shop Manual that Cadillac in that year used an elaborate "gasket sandwich" for the AFB. 

 

All information welcome.

 

Bill Shields (VA)

 

 

 

image.png.0739130624da3f42eb53077952fd73e4.png

Buick Nailhead 364 401 425 Carburetor Base Gasket 57 58 59 60 61 62 63 64 65 66

 

 

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I will attempt to take a look at my old stock gaskets off the AFB 2507S on my 1957 Roadmaster.  Incidentally, the off idle stumble of which you refer to could be the result of alcohol fuel usage depending on the amount ratio % of alcohol.  One cure for this has been the the little known art of enlarging of the AFB Idle Channel Restrictor to cure lean off idle stumble.  Also recurving the distributor in conjunction with the use of alcohol fuel can solve a lot of problems that reoccur for folks on this site :

 

335629479_CARBEnlargingAFBidlechannelrestrictortocurelean-offidlestumble.jpg.bd018b2c644a1f45ab3334511dcc5722.jpg

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I've been using a Mr. Gasket heat dissipator stack on my '65 Skylark with a factory AFB for over 15 years.  It has bolt holes for both carburetor bolt patterns and is wide enough to seal the carb to the manifold; additionally, it helps with heat soak.  Obviously, heat soak is worse than it used to be with modern gas, and I've found that AFBs are susceptible to it anyway.  I use a gasket on the bottom, but I also do not use a heat riser.  The exhaust doesn't seem to damage the gasket badly, but I replace it every five years or so anyway.  It might be worth a look.  I've been warned in the past not to overtighten the carb nuts when using these, but I haven't found that they unduly compress or anything.  

 

Regarding your vacuum leak with the correct gasket...I'm not sure about that.  Buick often used the gasket with the holes for the exhaust crossover with a metal plate underneath it; I tried using that on my '65 once and the car heat soaked badly.  A narrow gasket like the one pictured at the top causes a big vacuum leak.  You may want to go back to how it was set up before you switched carbs to eliminate that as a variable.

 

https://www.jegs.com/i/Mr.+Gasket/720/98/10002/-1?gclid=CjwKCAjwjuqDBhAGEiwAdX2cj8HgfFdgx9VRhVsHNh_fq3RQ34kXQgrt5WJJP7ChmWnFP7Qek3mqVRoCNCkQAvD_BwE&__cf_chl_jschl_tk__=b0f96c5159b26ac2317403b0e584664fd69bc5b9-1618659143-0-AZAmJUFcRXtrQyotjunerv-Wm9TRbvM85ZtmskdM8Gyz7jraySOpMM_a8icTYBi9RE92eFwZ4Bdjf7LuN8deuvBsQiFJ89HCINv0ajZJYzmjDd7o-vhigeASSGJ1SriVsQY2REwLXoR2LWb863Qt3bIJRRV-JOVgfWXVuw-JCg2LuM_yv_FmlnJ0krDURJlYq0IJL7KQSdBGVMYDlAEheqx-4LLoqJyRcYUUG8FyFDL4s1OJAS65l7fhIjszxUdkC-AgjNvKV0KUL3FLMSmzhMYsFOT-f461_la9p9cGwQSVjk7O5CtkT6OrmCd6KfK4uQNNpv4f-9DyhXZjnYE8LlCovOfUdG9q6s4AgurHwJJIKfAuO9gpM19ftGkYBnZP2l0EgPR79Flu88RvdlHbYlMeEZCXJaIAQw5MfnLlFV4iE35Z80a11vycbY-yamDtzBOcGl2_xuAHbqR_g0TPkV3f87cMHt7HpiCSMYbVcCu9XcUps7fat8gq31MVgFwuU8rDW5qNNBICzQiuMLE09YW6rMHaB9OBvSfANqFUkmqx

Edited by Aaron65 (see edit history)
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Correct gasket for the 1958 Buick Roadmaster with Carter AFB is Carter part number 1A-119.

 

The lower gasket in your post with the heat channel appears to be a replacement for 1A-119.

 

What you called a metal shim is actually an "exhaust heat baffle".  The heat baffle blocks any exhaust, but not the heat, which is conducted through the metal.

 

Impossible to tell from the pictures, but it is quite possible that the use of the incorrect gasket would cause a leak on each side right at the extremities of the heat channel in the carburetor.

 

Anytime one uses either a different than original carburetor, or different than original mounting gasket; one should first fit the gasket to the manifold, checking for leaks, then fit the gasket to the underside of the carburetor checking for leaks.

 

Jon

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Thanks to all for the replies!

 

Jon - I’m not sure what the last part of your message means about checking for leaks. Are you talking about just eyeballing the fit of the gasket to the mating surface? Or some other method?

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The eyeball test.

 

Compare the gasket first to the intake manifold mounting surface, then turn the carburetor upside down, and lay the gasket over the mounting surface, aligning the bolt mounting holes. Now observe  all of the various passages, and make certain none are open to the outside.

 

In the FWIW category, there are a number of different mounting gaskets for both Carter and Rochester with cutouts for the heat. They are NOT necessarily interchangeable, and often an incorrect one is in the FLAPS kits (which is why I mentioned that your gasket pictured APPEARS to be correct).

 

Jon.

Edited by carbking (see edit history)
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Jon - got it. I verified this morning that there is a leak. Spraying the base with carb cleaner test positive. Rag over the air intake test positive. In both cases idle and vacuum climbed.

 

I have another problem. The remanufactured AFB I bought some months ago from The Carburetor Center for $600 seems to have a defective choke adjustment. After multiple tries the car wouldn’t start this morning in cool 50 degree weather and on checking the carb I found the choke plate hanging open. The choke is set correctly at index, yet I had to flip the plate with my finger to get it to close fully. On the AFB I just pulled off, sitting on my bench, the choke at the same index setting snaps fully shut under the same conditions. 
 

I plan to message the seller this morning. For that cost it should be set right. Thoughts?

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On the fault choke issue ... The seller (via eBay) replied, “you need to adjust the choke a little more rich due to the climate difference between California and Virginia.” In other words, he suggests adjusting the choke when the outside temperature changes. I tried to tell him why that’s a ridiculous idea on a supposedly rebuilt carb. I told him that the choke plate should always close on a dead cold engine unless you’re in Death Valley. Also, fast idle wasn’t set right either because when I started the car “manually” so to speak, there was no fast idle, probably because the choke plate opened too far. And they claim they test the carbs on engines before selling!
 

His eBay listing says “no returns” but he’s offering a swap which I reluctantly accepted. I wonder what I’ll get in exchange. I have a 100% rating on eBay over 3,000 transactions, so in a pinch I think they would back me up. 
 

Word to the wise: don’t buy the Carter AFB for 57-58 Buick for sale on eBay. 

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The automatic choke, if everything is in proper working order, and correctly adjusted; should just plain be left alone.

 

The choke should be adjusted such that the butterfly just touches closed with no tension, when the ambient temperature is between 65 and 70 degrees F. If the ambient is colder than 65 degrees F., there will be some tension on the closed plate. If warmer than 70 degrees F., the plate will not totally close.

 

Automatic choke article

 

Jon.

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On 4/16/2021 at 10:50 PM, Bill Shields said:

Do any of you '58 experts know what the correct gasket arrangement is for the Carter AFB 4-barrel carb? Today I pulled off the manifold of my Roadmaster a clean, used, but not rebuilt AFB I installed back in 2014. This carb started, idled and ran well at speed, but of recent had developed a bad flat spot coming off idle. I decided to swap the carb for an identical, professionally rebuilt unit I 've had on the shelf since last year. The issue I confronted halfway through the swap has to do with gaskets. On the car (probably since I bought it) was a sandwich of the gasket shown below (note the cutout for the exhaust passage) on the manifold side and a thin stainless shim on the carb side. This shim has no cutout for the exhaust passage, hence that feature would not work. (Frankly carb icing is not a concern for me.) I opted to drop the metal shim and just use the pictured gasket. (Note: the gasket that came with the rebuilt carb was a plain paper item, pictured below, that also would have blocked the exhaust passage.)

 

I finished installing the rebuilt carb and started the car. It runs well at higher rpms with steady 17 inches vacuum. It runs unevenly at idle and vacuum is unsteady around 13 inches. I suspect a gasket leak, and will run some checks for that tomorrow. The question is, what gasket or gaskets/shims did Buick use? If that information is in the Shop Manual, I can't find it. Likewise zero info in the big parts books. I did find in my 1959 Cadillac Shop Manual that Cadillac in that year used an elaborate "gasket sandwich" for the AFB. 

 

All information welcome.

 

Bill Shields (VA)

 

 

 

image.png.0739130624da3f42eb53077952fd73e4.png

Buick Nailhead 364 401 425 Carburetor Base Gasket 57 58 59 60 61 62 63 64 65 66

 

 

The metal piece should be installed and came on these cars from the factory when equipped with Carters so that the aluminum base would not get eaten away by exhaust.  It has always been sandwiched on the bottom on ones I've taken off.

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Yes, I found a diagram in a Cadillac shop manual that shows a sandwich of (starting from the carb base) metal shim, gasket, heat dissipator plate, gasket. I’m not going with the plate as it would misalign the carb with other stuff. The manual advises some gasket cement between the carb and shim. I plan to use Permatex #2.

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