72 Duster: You can lead a horse to water, but...
Just for the heck of it, I decided to take the first Holley apart and see if there were any obvious problems. There were none. the primary float had no holes in it. The needle valve was clean and moved freely. I sprayed carburetor cleaner through all the passages and nothing was plugged up. I put a Demon carburetors primary metering block in and bolted the bowls back on. I put this Holley on the Dart, a car that seems to run consistently good even though it sits a lot.
It fired right up and ran as good as it always does. All along, I could have just worked on this Holley when it was in the Duster. It would have kept me from doing the intake swap too.
I often seem to learn the hard way.