Hello. I have a 1969 El Camino with a 350 eng., stock manifold and an Edlebrock Quadrajet spread bore. I took it to a shop awhile back and they discovered that it had a blown gasket under the carb. They fixed it. I took it out on the freeway a few days ago and got on it to get rid of some carbon. After that it started running lousy. I listened around and heard a vacuum leak around the base of the carb. I took the carb off and it looks like the gasket itself may have been leaking. My question is that it has a 4 hole gasket with a closed center on the bottom. Above that it has a 4 hole metal gasket with a closed center and above that it has a 1/4" thick open center heat insulator. The center of the bottom gasket was almost entirely burned away and the metal gasket center was partly burned away. On the front of the intake under the carb there is a channel that runs left to right and I see a trail of carbon from this channel back under the center of the gaskets to where they are burned through. I am thinking of replacing the 1/4" thick heat insulator gasket with a closed center 1/4" heat insulator gasket so that the centers of the thin gaskets would be sandwiched between the carb and the intake. Does this sound right? Does anyone know what this channel is on the intake? Please see the attached pictures. Thanks for any info you give give.
Thanks Techinspector. I just order the parts from Quadrajet. I still want to know what the channel is next to the primary ports.
11-17-2011 08:05 PM
Channels by primary bores are for idle bypass air. If your carb has idle bypass air there will be small holes .050-.080, sometimes bigger at the end of the channel. Sometimes the holes are at an angle into the edge of the primary bores themselves. This system allows additional air at idle which is really useful for big cams with low vacuum signal. Air is sucked in through voids adjacent to the primaries on the underside of the air horn down through holes in the main casting to the baseplate.
11-17-2011 10:44 PM
Streetbruiser. When your talking about the bypass air are you talking about the channel on the carb base by the primaries or the channel on the intake by the primaries? I went back to the Quadrajet wedsite and it says to put the stainless heat shield gasket directly under the carb and on top of the 1/4" spacer. It seems to me that the heat would be coming from the manifold and not the carb.
11-18-2011 09:41 AM
I was talking about channels on the baseplate. I thought that's what you were asking about.
11-18-2011 12:01 PM
I started out talking about the channel on the intake but this is good. Now I know what the channel on the base plate is for. Do you think that stainless heat shield gasket should go on top of the 1/4" insulator as Quadrajet says or below it? I think maybe they misspoke. As bnun12 said I would think it would go under it.
10-12-2012 11:25 AM
the heat riser valve at the end of your exhaust manifold helps to allow exhaust heat to pass up thru the channel under carb to help when the engine is cold.