Mopar Muscle Association UK

Just took the shooter off my 600cfm carb, the one in carb is a 31.
To see if this is the cure for my backfire my car has always had trough carb should I try bigger or smaller?

What makes you think it's the shooters? I'd put them a long way down the list of suspects personally.
I'd check timing, dodgy plug or lead, bad earth somewhere in the ignition.
If you're sure it's fuel related, float levels, float valve seals, air leak, mixture screws, sticky power valve...