carburtor gasket for '74 eldo convt.

[Viator Trudeau]

I traced the bad idle to a vacuum leak under the carb.  I do not see that gasket in the manual.
How thick is it and is there a s.s. plate on top of it?  Last owner installed a rebuilt carb. Bolts are tight and starting fluid sprayed there stops the rough idle.
V. Trudeau

[Dave Shepherd]

Quadrajet gaskets can be obtained at any parts store. No shim used here.

[TJ Hopland]

I think it was 67-69 ish that had an exhaust port at the carb base so you had to be sure to use the correct type of gasket or it would burn through.  That went away with the introduction of EGR which I think was 73 for most cars so there should not be anything special about that gasket.  If the choke seems to be working well now you want to get the same thickness gasket for the replacement. 74 was the last year for the choke to be mounted in the intake so a thicker gasket or spacer will alter how the choke works. You don't need to pull out the micrometer to check it just don't buy an extra thick or spacer one.

Parts stores should still stock these.  You can usually get them from the 'performance' section too.  If you get it from there be sure its for a Q-jet, not an Edelbrock.  The Edelbrock carb layout looks the same but the secondary (rear holes) are slightly smaller than the Qjets.

Its also possible that in the past someone over tightened the mounting bolts or even the top bolts and has distorted the base of the carb and that is what is causing your leak.   A check with a straight edge may be worth the trouble.  Throttle shaft bores also wear with use and can leak quite a bit too.  Those can be repaired with bushings by a good carb shop.