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What are you getting TO the start solenoid lead from the battery?
Are you still only getting 11 VDC to the new pump?
Perhaps to some extent, but there should be a constant voltage to the pump all the time. That can be from any number of things..........a dirty connection or battery issues. Try to eliminate that first. If this has been sitting any length of time you ca get debris from the gas going bad.
Then I suspect that the carb needs a good cleaning...........and you would get some minor voltage drop, but not usually 2 volts UNLESS the batteries are failing and you aren't plugged into shore power. I would test that as well. The charging voltage should be about 13.7 VDC, but just the converter alone can't supply enough amperage for starting this.
Just checking back it to see if you got this sorted out or do you still need some input from me here.