Sounds like low fuel level in the carb. Maybe sucking air somewhere or the pump isn't putting out the volume it needs to fill the carb. I would get it running for a minute or so then check the fuel level in the carb or put a pressure gauge on it. Or just pull the line off, put it in a catch can and crank it to see how much volume is coming out.
Thanks for the ideas, I'll go back over all the connections and check the fuel pressure, it came with an AFB installed so checking fuel level will require removing the top of the carb, I was going to do that anyway just to make sure it didn't pick up some trash somehow.
