I suspect the fuel tank charcoal can/tank vent isn't working. if I tighten the gas cap (yes the right one)the tank over pressurizes and it runs rough.if I leave it a little loose ,no problem.is there a way to test/repair this ?? are parts available??

 

Check the vent Valve. their is a line coming out of the tank with a Valve at the end that supose to let the tank breath in an out.

 

I'm chasing the same problem with the over-pressurized tank. There is a write-up on checking the canister and purge valve. Do a search and and you'll find a lot postings about high gas tank pressure, but very few solutions. Seems there are multiple causes.
One thing to check, and I would be curious to know the result, is the pressure in the line coming from the tank and going into the canister. When the car is hot with the gas cap tight, loosen the rubber line from the tank at the canister ( be careful, you could have a lot of pressure) and see if it relives some pressure in the tank. When I do this on my '88 Formula, I get no pressure, only a very little gas vapor coming out, I think that line is clogged somewhere back in the tank. I've gone through canister purge valve and solenoid checks, everything seem ok. If you find a solution for your problem, I'd be interested in the details.

 

Yeah, I replaced that on mine before I found out that it only lets air into the tank to keep it from developing a vacuum as the tank is drained, not to vent pressure out of the tank. There is supposed to be an "in tank" pressure control valve that vents vapor to the canister. I think it's part of the sender unit assembly with the 4 pipes coming out of it but I'm not sure. That might be the source of my problem.