[CGalbus]

I have an issue with my 1969 GTO 400 engine that has a 1967 intake manifold installed on it regarding a vacuum issue. The issue arose when I attempted to use my vacuum-assisted brakes and the car didn't stop very well.

Currently, I am reading about 5 in of Hg at idle (idle is set at 1000) and when revving the engine up to about 3000 I get about 10 in of Hg. I also performed a test that I read about where you partially block the airhorn of the carb and see what happens, my engine revved up higher which told me that there is a vacuum leak.

I have narrowed down the location of the vacuum leak to around the base of the carb (I have blocked off every other vacuum port with rubber stoppers). I believe my leak is around the carb as when I spray starting fluid around the base of the carb I hear the revs jump up. the revs also jump up when I spray the vacuum-assisted choke installed on the carb though I have read that on some carbs there are purposeful vacuum leaks to allow the choke to suck in cold air to work properly.

I have a couple of questions regarding the carb...

1) Could my gasket be wrong (I will attach a picture of the previously attached gasket which looks like part of the intake does not fully adhere to it by looking at the cross-over prior to the smaller holes.

2) Is it normal for the choke to be sucking in the starting fluid and increasing the revs or do I have a secondary leak here?

3) Around the base of my carb I notice what looks like gaps. Is this due to me using the wrong gasket or is this normal?

4) I also have an aggressive cam installed and am worried that it might be playing a role in all of this.

Additional information:
Car- 1968 GTO body
Engine - 1969 Pontiac 400 with a 1967 intake
Cam # - 51-234-4 (Comp Cams )
Carburator # - 29268WF 1209 - bought from a Pontiac tech who rebuilt it.

Pictures attached are
A picture of the carburetor number
A picture of the choke
A picture of the old carb gasket
A picture of a gap in between the carb and the intake.


Thanks for helping me out!

[Sirrotica]

67 GTO and Firebird 400 had a one year manifold that heated the bottom of the carb with exhaust gases. They had a stainless plate that kept the gasket from burning up. If your trying to use another year base gasket it won't seal the heat channel, and you'll have a vacuum leak, such as you already have.

Picture of what you need for base gasket and plate:



In your second picture you can see the carbon between the primary bores here your leak is, hopefully this will solve your problem.