Try enriching the main jet screw 1/2 turn and see how it acts after you check the fuel flow as suggested.
Also,
many times a piece of foreign material ( IE.fuel line hose) will become lodged in the fuel inlet fitting at the carb that leads to the needle valve.
Does pulling the choke help?
Another thing comes to mind:
A bad condenser can and will allow an engine to start normally and idle
at slow speed all day long,
but when the throttle is advanced, it will not rev up and will act like a fouled plug/missing/sputtering.
