72 Duster, Ethanol gas, intake backfire

Kern Dog said

I had to spray carb cleaner down the throat to get it to fire

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Carb cleaner is not starter fluid. My dart sat in so cal for 4 years with a half tank of standard off the shelf gas. After a shot of starter fluid it fired right up. I filled the tank with new gas and put 200 miles on it. Filled it again. A few months later I changed the sender and except for a handful of rust spots in the tank it was clean as a whistle.

I couldn't agree with mattax more. if no spark at the wrong time or an open intake valve , no backfire.

I had a dist that had do much up and down slop it would throw spark to any number of cyls. I suspect the rotor would make and loose connection to the center of the dist cap. I put the oem dist back on and the backfire / miss went away.