Hi, sorry to hear that, what i'd try now is disconnect the petrol pipe from the carb,and run fuel into a milk bottle until at least half full, you can also see any muck in the fuel. It's to check the CONTINUOUS flow of fuel, if the flow slows down during this test it means there's muck in the tank or that the tank cap breather hole is blocked therefore causing fuel starvation after a set time.
If that fails I would very carefully check the floatbowl,float & pivot pin, float needle & seat for obstructions and smoothe working.
Chris P.Duck
July 2010