Track down a vacuum leak?

[Dave Rifkin]

I recently purchased a 1969 Corvette coupe. Shortly after purchase I took the car to a well knkown Corvette shop in the area to have them tune the car up and give it a once over.
Before taking the car there I noticed that the car idled rather high after warm up; like 1100 rpm's.
When I got the car back it ran better but, I was told the idle is still high. The shop thinks the car has a minor vacuum leak which is preventing them from being able to properly set the idle.

1) Does that sound right to you guys?

2) Is there a easy way to track down a vacuum leak?

BTW: the carb is a Quadrajet if that makes any difference.

[VintageMusclecar]

With the engine warm and idling, go around the intake/cylinder head mating area as well as the base of the carb and the throttle shaft areas with a can of carb cleaner. If/when you find the leak the engine will draw the carb cleaner in and you'll hear the engine "clean up" momentarily.

You might also verify that the correct carb mounting gaskets are in place, and that the throttle shaft bore isn't worn loose. Lastly, go over all the vacuum lines to make sure none have fallen off, split, or otherwise deteriorated.

Eric

[njsteve]

If its the original 69 with a Quadrajet it has the two piece carb to intake gasket. One piece is the thin metal heat shield and the other is the gasket. The metal heat shield goes down first against the intake, then comes the gasket. If you leave the metal shield out you get a vacuum leak from the heat riser. It usually wont show up when you spray the carb cleaner around the base plate because it's sucking vacuum from inside the engine not from outside. I would pull the carb and verify the correct 2 gaskets are in place.

[Dave Rifkin]

njsteve; are those gaskets required for the Quadrajet or just what came on the cars originally?

[njsteve]

Both. You can't run the car without them or the vacuum leak occurs. They were original equipment. I had the same problem on my 69 350/300 Z11 when I first got it running. I originally installed the gasket without the steel shim on the bottom and it idled at 1200 rpm and ran like crap. Someone gave me the same advice I gave you and voila, it fixed it.

[Dave Rifkin]

Can I get the correct gasket at any auto parts store?

[Salvatore]

Yep. Don't let them make you buy a whole kit for 1 gasket or we will get BBBenny to take care of your lite work with no problem!!

[HEMIBEE]

if the gasket doesnt look to be the problem, go to a chevy dealership and see if they have a smoke machine. i have one at my shop and it is a life saver at times, it produces smoke and you can pump it into the intake or crankcase or exhaust depending on what type of leak you are looking for and you have no threat of a fire from the carb clean. Rich

[169indy]

Z15 I found the following avail from the (IRONIC) Holley catalog
Base Plate, quadra-jet, bore size: 1-3/8" primary, 2-3/8" secondary, thin stainless steel. PART No. 108-20

I had left mine out and trouble shot the eng for a while before figuring out the metal gasket was missing. 6$ back in 1987. As Steve had mentioned the intake charged is fouled with heat riser gases, Soots up the plugs is one indication, in addition to poor under load performance.

Hope this helps.

Jim

[Dave Rifkin]

Aside from the high idle what other symptoms would the lack of this metal gasket create?
My car has very little low end torque; at least it seems like that to me and it just doesn't have the balls that I'd expect from a L46 car.

Once I replace the gaskets with the correct ones; assuming the car has incorrect gasket set, what steps do I need to do? Do I simply adjust the idle speed and I'm good or is that being a bit too optimistic?