I've seen a recurring problem on some Q-Jet installations, and though I would share this info with the Forum....

Problem & Symptom: Q-Jet is a piece of junk!! It won't idle right, idle speed is erratic, idle mixture screws don't work, car has a big hesitation off idle, it surges at cruise, and sometimes the engine even overheats.

Solution:
Early Q-Jet Vettes (late '60s) use an exhaust crossover passage in the intake manifold that runs just forward of the primary throttle holes in the manifold. The photo below shows this passage on a '69 427 Vette:


Often, people will install a standard carb gasket first, then a metal heat shield plate, and then a second carb gasket to seal it all up. If this is done, the standard carb gasket will burn through, and you will end up dumping exhaust gases right into the intake manifold. All the symptoms listed above will occur, ad you can rebuild and tweak the carb all day long with no results whatsoever.

To prevent this, you MUST use a special composite gasket on the manifold. This compositie gasket, NAPA Part Number G14579, is a metal gasket with a high-temp coating on both sides. It has a cut-out for the heat passage. On top of this gasket, you must use a steel heat shield. On top of this, you can then use a standard gasket. Photo below show the gasket "pack" that must be used with this setup. The gasket on the far left is a "wrong" gasket: it cannot be used as a base gasket. in the middle you see the composite NAPA gasket on top of the metal shield, and the upper gasket is to the right:


If you have an early Q-Jet car that's running like garbage, be sure to check the carb base gaskets before you throw the Q-Jet in the trash....



[Modified by lars, 1:32 PM 10/22/2001]

 

Lars, I remember dealing with this issue when I replaced my carb. I think I got it right - I know I have one layer that is the metal plate/heat shield that covers the groove. It took me a long time to realize there were actually holes in that sooty little groove!! Also, just in case some of your readers are gazing down the primary throttle holes looking at those "grooves" or ridges, lookie here!! =>


There are 2 little holes at the ends of that black up/down groove. Joe Lucia recommends sealing them off with pipe plugs. Even if you have it all correctly installed the hot engine gases will tend to cook your carb. Hasnt been a problem for me yet. MJ

 

if the manifold is on the engine just use steel cup type soft plugs to seal the crossover. that way you get no chips in the passage which can end up in the engine. :chevy