In reply to ashaw:
Sounds like fuel starvation to me, will it tick over ok and when you twist the throttle it dies?
Was it standing for a while prior to you buying it? of so then the fuel may have gummed up in the carb in which case you will need to strip it and make sure all jets are cleaned with an airline, while you are at it make sure the fuel tap or vacuum diaphragm isnt blocked. Also check the float height is correct.