Bongo Fury

I get a fair amount of pressure from the tank when releasing the filler cap. The evap solenoid works (I get 8V on the connector for a second or so and the valve opens then closes again).
Can the canister itself fail or become saturated? My Jap bikes all produce a good hiss when the cap comes off in this weather but they don't have a captive evap system so is this normal behaviour on the Bongo?
Engine runs well and idle is correct and smooth.

I have a 2.0 too and noticed in hot weather the cap likes to hiss when removed, it also seems to do it more, the less fuel there is.
Its done this ever since i got it so i'm guessing its normal. Also i work on cars petrol and diesel and all the petrol ones seen to do the same so fingers crossed with this.
Sorry i cant give a definate answer and i hope this helps