This past weekend I did some tuning adjustments to my Edelbrock 600 #1405 in an attempt to lean it out a tad more in certain areas. Using the calibration kit I changed both primary jets and metering rods as outlined in the calibration chart. In the process the airhorn gasket tore slighty or more accurately delaminated while removing. It didn't appear serious and without a replacement gasket on hand I reused it and fired the car up.

Initially the car ran fine and my rich zones were improved. I ran the car for about 8 miles, came back home... washed it, waxed it and prepared to go to the Car Craft Summer Cruise in St. Paul (about 30 miles away).

Car ran fine when I got it out on the freeway but upon arriving at my friends house close to my final destination, it idled rough/stumbled and would not smooth out until after 1,500 rpm. Even then it appeared "not up to par". I checked timing and it was still fine. Could the airhorn gasket (after the car warmed considerably) be leaking creating a vaccum leak? It runs as if a vaccum line is off, but I've checked all and they appear fine. I can also smell gas upon shut-down so I'm wondering if the airhorn gasket is the culprit. There is no pooling of fuel anywhere, but I'm assuming if there is a leak it would evaporate quickly.

I'm going to order extra airhorn gaskets today along with an heat insulator gasket as I'm experiencing hard restarts (no surprise with the Edlebrock) due to has percolation.

Any insights guys?? Thanks in advance.

It sounds as if it after a real drive, it got hot enough to be a lean condition now, ( lean is hotter) and would explain some perculating from the carb into the intake after it has been shut off giving you a gas smell and hard starts. look insidethe carb with a flashlite for even a tiny drip of fuel befor you shut it off and after from the main metering if you do see fuel try to richen up Idle 1/2 turn each and take it for a ride (keep Idle as low as you can ) , if better than that is probably it. Although a new gasket is in order anyway. It could be a air leak causing you to be lean on fuel , so put the gasket on then drive it if still an issue richen Idle a LiL at a time. Keep in mind a mixture change also changes the speed of the burn in the cylinder you actuly are changing timing too.

Had a little time tonight to do some more investigating. It appears I have a lean condition (possible blockage) on one side of the venturi in the carb. Cylinders 1, 4, 6 and 7 are not firing or are barely firing at idle as those header pipes are considerably cooler to the touch than 2, 3, 5 and 8. I can't recall which plane in the dual plane manifold those are on, but I think I have it narrowed down. I'm waiting for new air horn gasket before I go in. Any other comments on where or what to look for??? Would the blockage be within the bowls at the primary jets, metering rods or should I be looking at the idle circuit???

ttt

Use a temp gun and shoot the headers. Typical temps are above 500*F.

If you have anything lower, you have a vacuum leak, e.g., I would suspect a leaky manifold gasket. If you rev the engine up and exhaust tube temps come up, a good sign of leaky manifold gasket. Change it.

Air horn gasket, I don't think, is going to make a difference as it is above the throttle plates.

Agreed, but the high temp/low temp header pipes is married to the dual plane intake manifold... this leads me to believe this is carb related not intake. It would be too perfect to have intake leaks on all the same cylinders which are on the same plane of the manifold.