Again: Unleaded or leaded fuel for mid 70's /6?

Ethanol is a problem for carburetor cars. These carbs were designed at a time when they had vented fuel bowls and gas had a bunch of stabilizers in it so that the fuel would evaporate less readily. Once cars all came with sealed fuel injection systems, the gas makers did away with the stabilizers. This is why, if you let the car sit for days it takes a lot of cranking to refill the bowl and start your car. Ethanol is hydrophilic - it attracts and holds on to water. Gasoline evaporates more quickly than ethanol, so in your fuel bowl the concentration of ethanol rises as gas evaporates leaving ethanol. The ethanol and water sit in the bowl and react with the metal of the bowl and develops a gooey mixture of water and corroded metal and when you start the car that ends up in the small passages in the carb. (this is even more prevalent in 2 cycle engines - mowers, chainsaws, etc, which is why you should NEVER use ethanol gas mix in them!!!). There are a number of products to put in your gas tank to change the dynamic so that the ethanol doesn't hold the water. The one I use is called Carb Defender from a company called Driven.