The motor stops after about 90 seconds and is pretty hot even when not run hard. I have tried adjusting the mixture running it leaner and richer and it makes no difference. I think its a fuel problem, perhaps vaporising

sounds like a plug dude.... if you leave your glow wand on it and its fine then dies shortly after taking the wand off its def a plug.... if the fuel was vapouring it would have the "lean" signs all the time.... i take it you have checked for air leaks etc? ie pull the fuel lines off block the outlet with your finger and blow in the inlet... if it leaks replace th "O" ring on the lid or get a new tank.... any fuel leaking from anywhere on the motor? have you sealed it? all things to consider.... but at this stage im going with a farked plug....

checked for leaks.
the plug is new :O

i have had a few issues with brand new plugs being bad out of the package.... if your convinced there is no leaks try another plug..... or pull down the carb and clean the needles... i use contact cleaner to flush out my carb... eats nitro build up real well... just wach the rubber o rings it will harden them....the other thing that can block is the fillter in the bottom of the fuel tank pull the lines off and blow through the line and see if a good rate of fuel is coming out the other end....ummmm bout the only other thing is your idle setting??? how far open is the carb slide when its closed and you look down it? (after pulling the air fillter off)