I'm more of a paint/body guy - not the sharpest with engines : I can get fuel to the carb if someone holds the butterfly closed , simply cranking over isn't pulling enough fuel to fire it off - doesn't want to stay running either. Just bolted a new carb and fuel pump on. Had the same issue a few months ago and found crack in fuel line (sucking air) acting the same way except fuel will make it up with butterfly closed ..... where should I look for a cause this time ?

Double, triple check for any leaks on the suction side.

Make sure the sock in the gas tank is not clogged.

Be sure the tank is vented properly.

hook a can of gas to the pump inlet w a neoprene line & retry it. That'll tell you if the prob is in the pump/pushrod (BB)/carb filter or if it's rearward in the hard and neoprene lines