Fuel Pressure Issue
 

I have a 1982 RX7. The car has only 45,000 miles and is rarely driven. After driving I hear a high pitched whistle coming from the gas tank. When I remove the gas cap there is a lot of pressure that escapes from the tank and the whistle goes away. Is this high pressure normal? Is the tank suppose to be venting in some way but is not working properly?

As you surmise, the tank vent is plugged up. There is a check valve mounted beside the tank that leads to a nipple on the top of the tank. This then connects to a hard line that runs up to the front of the car and to the charcoal canister/airbox lid. Somewhere in this system, there is a clog.