The second line is a pressure line. It will have a check valve in it somewhere and it's purpose is to use crankcase pressure to keep the fuel tank slightly pressurised, in order to keep fuel delivery constant whatever angle the machine is being operated at. For this reason, the fuel cap must be airtight. If it wasn't before you started this exercise, put it all back cos there's nothing wrong with it - get a new gas cap!
Phil Saunders
November 2007
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