Yesterday I got my 302 running with f303 cam. It had a holley 750 dp and would driwn the spark plugs. Switched to a holley 600 street avenger today and it won’t stop throwing fore out of the carburetor. Nothing changed exept the carburetor. Upon inspection it looks like my distributo cap has a crack in it. Can a crack in the cap cause a backfire out of the carb?