I found 4 things that can cause the gas tank to build pressure so when you remove the gas cap you get a lot of air released. There is the solenoid on the intake, the check valve between the cannister and the tank and the cannister itself. There is also a vent valve that is in a remote spot. Does anyone know where this is located and what it looks like? Also, if you had this problem what part turned out to be the problem for you or what part(s) usually gets plugged or breaks? I guess the lines can get the charcoal in them and plug them up also.

 

http://shbox.com/1/fuel_pump_wiring.jpg

 

Once again my question answered better than i thought it could be. I checked your site and missed it i guessed. I better pay more attention or look a little better.