Fun with carb base gasket

[rpmerf]

Ongoing story of my fun.

1970 C20 350, Quadrajet from a 1973 truck. The truck had been owned by my uncle from 1987 through 2011 when he gave the truck to me.

I took the truck to a car show at work about 3 weeks ago. It barely made it home. Sputtering, doesn't want to accelerate. Intuition told me vacuum leak, so I grabbed the carb cleaner. I found a leak around the passenger's side of the carb. Guess it needs a base gasket. Pull the carb off, look at the gasket, search around for a couple hours and determine it's a 1975-80 gasket. Don't know why I have a 70 manifold with a 73 carb and a 75-80 gasket, but whatever, it's been like that for the past 8 years. I find one at a local Advance and buy it. I ordered 3 off RockAuto, so I have some spares. Install it. Still changing RPM when I spray the pass side of the carb base, but it's better than it was. It drives like it always did. Figure I'll give it a couple heat cycles and retorque it and see if that helps. That takes us to today. Check it again, still leaking. Retorque it, still leaking. Figure I'll try coating the gasket in a thin layer grease to help it seal. Still leaking. At this point I realize something is not right. Take off the carb, line up the gasket, and there is an exposed vacuum port on the pass side near behind the secondaries. I haven't removed this carb since I got the truck in January 2011. This carb has had a vacuum leak for at least 8 years! The truck and it has run pretty good. Maybe a little lean at cruise, but always fired up and got down the road. Just went on Rock Auto and ordered 2 different gaskets - an open plenum one and a 4 hole one. Both on wholesaler clearance, so I got 3 of each shipped for $12. Not sure which one I'll use but I figure the 4 hole one will work better with the stock manifold. Can't wait to see how much differently it will run without a vacuum leak.