What is the thing on the frame that goes to the carb it is up by the rad cap

 

The thing by your radiator cap is a fuel pump that is vacuum operated by motor pulse. One thing you said about melting the vent hose for the tank, if you sealed it could cause a vacuum on the tank not allowing fuel to flow. Try to start it with the gas cap off and you will have to crank it a minute or two for the pump to get fuel to the carb. I am not familiar with the pump but it could need priming before it will start pumping.