My son-in-law has left his 2003 VN750 in my garage for several months with the petcock on and fuel in the tank. We have drained the tank and replaced the petcock with a non-vacuum model. We cleaned the tank and put seafoam in it with the new fuel. Now it will start but when the fuel in the carb is spent the engine dies. Is this something in the lines or do we have a vacuum issue?