They are exhaust gas ports. That is a quadrajet manifold. The original theory is that by bringing some of the exhaust gases up into the carburetor base it would help heat the fuel mixture. Theory didn't work too well on hot days...vapor lock.
We discussed this last year late August or early September. Try searching for that thread.
Many offered opinions and it seems that you are best to tap and screw 1/4" pipe plugs into the 2 ports. That is what 2 carburetor rebuilders I spoke to recommended. There is also a block off plate that you can buy from Felpro. I can look up the number if you need.
I had a buddy that had a chev 400 van that had to take it in to get those holes cleaned out as the 400 would start fast idle all the time and got to the point it wouldn"t cut down? so I am not sold plugging the holes off..?
I had a buddy that had a chev 400 van that had to take it in to get those holes cleaned out as the 400 would start fast idle all the time and got to the point it wouldn"t cut down? so I am not sold plugging the holes off..?
The fast idle is governed by the choke thermostat, which is not effected by plugging the holes on the carb flange of the intake. The choke thermostat would be effected by plugging the passages between the cylinder heads and the intake.
if you plug the holes up top, and im lazy so I don't take the intake off to put threads in, the heat from the exhaust still heats the cross over at the bottom of the manifold. if the carb boils , quadra junk stuff use a heat insulator underneath . as far as the fast idle that's another design flaw and needs to be address in you vacuum system when you rebuild it, it has very little to do with your heat cross over. as some of you well know I drive this stuff year round with this mods and now issues.
