Tom, Sorry to come in on this problem several days late and the other members suggestions are good. My only suggestion is to ask you when was the last time you changed your condensor in the distributor? Does the car also start hard when hot? I had similar symptoms you describe on my '56 New Yorker (almost a 300, there I got the 300 word in) and was about to rip the carb apart. Talked it over with member Tom White (also the owner of the only running '58 Desoto Adventurer Fuelie in the world) and said to change the condensor before doing anything else. I put a new one in and it immediately curred the problem. No backfire, hesitation, and runs like a 300! .........Almost Just my 2 cents worth, John R. Cote, Connecticut