They're a bugger of a thing. Mine used to run on for ever, I used to see how long I could keep it alive for, I think my record was about 20 seconds Make sure you have the fuel cut off valve in tight enough. And also check all the fuses, as there is one in there for the idle cuircut, my mate once had a problem with his and it blew the fuse every few days, I can't remember why. Also check that the ground wire from the Carb to the motor is intact.
It's all part of the fun and embarressment of driving a good old golf.