Heat soak? Edelbrock carb & air gap

You're very likely right, I've got similar stories I could share. Ethanol in gasoline has made the problem worse. An easy test is to find some non-ethanol premium and give it a go. One common bit of advise is to install a Phenolic carb spacer, personally I've never had much success or seen much improvement from adding one. Luckily I do have a convenient service station that sells non ethanol premium, the only sure cure I've found.

The above said, since non-ethanol isn't always convenient I've just added a Street Demon carb to the Duster with the poly body (the ignorant think it's a Thermoquad), seems to be a decent carb so far and it should deal with ethanol better that the classic AVS or AFB.

Good Luck, Ron