One of my 454/420's has been giving me trouble starting. If it sits for a few days, it will crank and crank with no start. Then after pumping it like crazy it will start, die. Sometimes when it dies it coughs smoke out the flame arrestor. After several tries and it gets going, it starts all day no problems. Also, this engine is down on rpms. It has a new fuel filter. Could it be a bad fuel pump? Its not pumping enough fuel when cranking?

You could remove air cleaner and see if it pumps fuel when you pump the throttle. If it does then there is fuel in the carb. Next I would look to ignition stuff, cap, rotor, wires, plugs and timing.

Verify fuel pressure with a fuel pressure guage.