Quadrajet gaskets

[drmiller1]

Hey There,
I have a 1969 350 with the stock quadrajet on it. I had this carb rebuilt. When I pulled it off, there were 2 gaskets that sandwiched one very thin metal spacer. The spacer cover the "shallow trough" in the front of the intake where the carb bolts on. I mentioned this to the rebuilder and he said to just put a single gasket back on, this leaves the "trough" open.
Now my engine will start and run, but idling is a problem. Should I put the metal spacer back in? Any ideas? thanks.
note:adjusting the idle screws does not seem to make much of a difference other than seated all the way in. This causes a stall.

[Shyguy]

If it were me I would put the metal spacer back on.

Then if the problem still exists I would look for a vacuum leak.

You may have to adjust the idle screw on the linkage to get the proper idle rpm.

Danny

[ChevLoRay]

Originally, they only had the single gasket (it's thick, right?). If I remember, the thin stainless was there due to the EGR system. The stainless gasket kept the hot exhaust gasses from affecting the carburetor. If you don't have EGR, then you may have another problem with the carb.

On Q-Jets, there are two plugs in the base of the throttle body that can leak into the intake. There is a set of replacement plugs that also have O-rings that replace the earlier style. That is one possibility. You may have also seen what looked like a piece of black sponge rubber in a kit. That piece fits in the bottom of the throttle body and is designed to hold those original plugs in place to also prevent leakage into the intake manifold.

If the intake is not an aftermarket intake, then it probably had EGR and you have created a vacuum leak. Somewhere behind the carb should be a mounting flange for that EGR valve. If it isn't blinded-off, you should get busy and get it "stoppered". It may be carboned-up enough that the vacuum leak is small enough to let it idle, but if it were opened up, it wouldn't run except wide open. Again, this is if my feeble, stroke-damaged brain is functioning on the right level.

Let us know.

[71 super]

You do have a vaccum leak with that trough. If you leave the thin gasket in place the trough will burn through it because the trough is connected to the center heat riser. Get 2 thin gaskets and put the thin metal back in place and you will not have any idle problems because you won't have a vaccum leak. Been there, done that.

[drmiller1]

Well 71 Super hit it right on the money. I installed the gaskets with the thin plate between and the idle smoothed out. From what I have found out, GM
used this setup from 68-69. Thanks for the help.

[ChevLoRay]

There you go....help when you need it from the person who had been there. Don't you just love this site?

[JimKshortstep4x4]

The "trough" is to let exhaust gas circulate under the carburetor but it has to be covered with the correct stainless "gasket" which should be sandwiched in between two gaskets.

Without the correct gasket in place there will be a bad vacuum leak.

If you look on the ends of the trough you will find two holes approximately 3/8" in diameter which go into the exhaust area.

This arrangement was eliminated in later manifolds.

I tap the two holes with a 1/4" npt tap and plug them as they can leak exhaust out from under the carb and you will not notice any change in the way the engine runs with the holes plugged.

Jim