What’s the height between the pump and the tank? Maybe try lifting the tank a bit by placing it on a box or something and see if the pumping improves. If it doesn’t, there might be a problem downstream from the pump to the tank.
A pulse operated fuel pump can only lift fuel so high and I believe around 30″ is considered OK for an outboard motor but don’t quote me on that figure.
If you can tee into the fuel line, prime the carb and start the motor to see how much fuel is being pumped under operating conditions. A few feet of clear plastic tubing attached to the tee and held straight up will give an indication of the pressure or volume the pump can develop. If it pumps well with the end of the hose placed in a container, the pump is probably OK.
