Well........I just might have stumbled upon something interesting. The metal fuel line that should be connected to the fuel vapor canister runs from underneath the car across the back of the firewall and then makes a right angle turn and runs parallel to the engine pointing to the front. Since I replaced the stock manifold with headers the fuel line is 1" from my headers and it is not closed off. Now the heat that is generated around my headers and in the engine bay must be being pushed back through that fuel line and right into the tank. Remember the fuel line is facing the front of the engine so while I drive the air is forcing all that heat right through that line. Wouldn't ya think? Read below what I found tonight and give me some feedback.
Fuel lines are placed as far away from exhaust pipes, mufflers, and manifolds as possible, so that excessive heat will not cause vapor lock.
They are attached to the frame, the engine, and other units in such a way that the effect of vibration is minimal, and so that they are free of contact with sharp edges which might cause wear. In areas where there is a lot of movement, as between the car’s frame and rubber-mounted engine, short lengths of gasoline resistant flexible tubing are used.