Will leaving off gas cap get air in the fuel line to need to have that purged? and or will running out of gas do the same thing? had both things happen and a mechanic had to purge the fuel lines-a few days later I ran to E on a tank and the boat did the same thing would not start after switching tanks but using some starting fluid I got it to start and run ok-how can I purge the line like the mechanics do if this happens again?