BTW, how do you have the 4 vents connected? I would actually plug all 4 to prevent dirt and moisture from being sucked in under the car and avoid any fuel spillage or expansion overflow, and go out an buy a 'for-sure' vented gas cap. Some of them have valves only vent above a certain pressure level IIRC; I had one that had been on my '62 for years with the PO, that was made to vent only above a pressure level; one day it decided to stick and 'foooom!' the gas tank got sucked in after driving 2 miles! A trip to the NAPA store fixed that!
