I've been having a problem where my tank keeps pressurising and killing the engine. After sitting for a few minutes it will restart but with the out of fuel symptoms. I've checked the breather but found it clear although I did find the (breather?) pipe that connects to the left side of the air box diconnected. Am I right in thinking this is a breather or does it serve any other purpose? Could this be the cause of my tank pressurising?
Any pointers much appreciated.

Pressurising??
It normally has a vacuum problem caused by the fuel being used and no air getting in to replace the fuel, this causes the pressure in the tank to fall. As the pressure in the tank drops the outside pressure tries to push the fuel back into the tank and causes the fuel starvation.
The usual suspect is the non-return valve that sits on the top of the front right hand side of the tank sticking shut, or the hose that comes from it is crimped somewhere along its length. It actually splits into two down behind the fairing on the left hand side to try and prevent a blockage.
Try this:
Remove the hose from the tank non-return valve and blow through it. If there is no resistance to your breath then go to stage two:-
Remove the non return valve from the tank and blow through the spigot that you removed the rubber hose from. You should be able to blow air through but not suck air back.
Let us know how you get on.

The "breather" on the left hand side is a drain, IIRC.

Thanks TonyB, the N/R valve on the tank was stuck shut. I was going to give it a shot of WD40 through the spigot but would this be advisable?

Have you freed it up now?
If not try this:
Get a matchstick or something similar (make sure it is blunt) and very gently poke it down the hole in the non-return valve and push the valve open. It should not need a great deal of pressure. After you have freed the valve a shot of WD40 would not do it any harm.

HTH

Tony

Cheers Tony, I've freed it now just by blowing & sucking on the spigot, not very nice, I'll whip it off again & give it a shot of WD.
Thanks again