A quick test just to rule out the kill wire is to push it down to full throttle while not running (a good shove, hard and fast) then gently pull it back to choke and start, if that does it, then look into the wires.
However, to me like a tuning issue, you can adjust the throttle positioning by lostening the little screw at the top of the air hose.
When done corectly, the trottle lever should stop about one matchstick short of the top of the slot.
Apart from that, thorougly clean the jets and fuel side of the carby, and check the priber buld for damage.
Have you done a work over on the carby, I usually find it pays to sit down for 20 minutes with the carby, a toothbrush and some old fuel, and clean it all up nice.
