Locking Fuel Cap

[scoutcamper]

Hey all,

I have a "new(previouly ignored)" issue on my 71 build. the locking fuel cap that i purhased from chevyduty (will link below) Leaks. When i go around a corner gas pours out of the fuel cap. We found a "non vented fuel cap" from a 72' parts truck that we picked up awhile back, and that does the same thing. Any suggestions to not leak fuel every time you make a turn?

the cap i purchased is http://www.classicparts.com/1938-71-.../#.UJqKBYaz6o8