Carb gasket, which one is used?

[55 cadi]

Hello,

When I bought my rebuild kit for my carb it had these two different gaskets, that go between carb and manifold.

Which one should be used?

Difference is one blocks a port and the other makes it open for the port in the carb, what's difference do the two make ?

I'm pointing at the opening in question

Right now I believe one like the one on the left is in there now, just want to know the difference and see if other is better for set up.

Thanks
Jason

[Steve Passmore]

Its not what's a better set up, its just that these kits now contain the gaskets for several different models of carb so they supply them all and you use the ones appropriate to your carb. Replace the one like you have in there already.

[craig-o]

Rather than just put back what was in there, I suggest that you look at the bottom of the throttle body and the top of the intake manifold to see which gasket matches.

I recently re-built my Rochester 4GC carburetor, and it came with the wrong throttle body/intake manifold gasket (like the one on the left in your photo.)  What I needed was like the one on the right, as you can see from the base of the throttle body.  I ended up ordering a complete kit for a Carter carb of the same year to get the correct gasket.

[fishnjim]

AS I understand it:  (from my '58)
That era has an exhaust port in the manifold to prevent "carb icing"* and that opening allows the hot gas to warm the carb.   If you block it off, no harm, no foul but may not operate well in cold climates.   
If you change carbs to a modern one, you don't use it.   The blind one is used or if you put the old carb on a newer manifold w/o.   Some have a thick insulator to prevent vapor lock which could be a problem if you are in hot climate and use the icing port.
* - idle is done with vacuum aspiration - there's a center air screw between the two jet screws and no throttle plate idle screw.

[55 cadi]

Thanks all,

Steve,
I don't trust what was there as the previous owner had a lot of wrong stuff on or added to car.

Jim and Craig,
Thanks, I was mistaken, I have the gasket on the right on it because when I had the one on the left I found excess gass on the gasket.

So I am using which seems to be the correct one.

Although one question arises which is fishnjim mention about using that gasket in hot climates might not be good? Am I reading this correct?

Because here in Texas is hot, but now about to get into cold.

Thanks
Jason

[35-709]

Use the correct gasket for your car, period.  Cadillac engineers figured it out many years ago for your car.  Just make very sure your heat riser valve moves freely and is operating properly.  The heat riser valve and the passage under the carb are designed to route hot exhaust under the carb to help warm it when the engine is cold for improved cold engine operation.  With a properly operating heat riser valve the exhaust gases are soon routed out the exhaust and not under the carb as the engine warms up.