350 sbc back fires please help

I am helping a buddy of mine with a 67 camaro with a 350. We just replaced the carb with a holley 670 street advenger as well as the plugs. The car keeps back firing through the exhaust. It sounds like it is back firing through the right side. We have done all of the obvious stuff. Any help would be great. Also I just had a gas tank for a nova boiled out and the guy at the radiator shop told me to coat the tank with a pint of transmission fluid before reinstalling. Has anyone ever heard of this? Thanks again.

Double check the firing order.
The tank is shiny clean, the oil will stop it from rusting until it' filled with gas. If you're going to get it running right away, it isn't needed.