Carb settings for a Suffolk Super Colt (Zenith Carb)?

I've just brought an old Suffolk Super Colt. It's been stood all
winter outside but after a little coaxing, I managed to get it to fire.
It won't run for any length of time, though, so I stripped the carb down
for a clean. It all looked in good shape, but the engine still won't
run properly. While I had the carb apart, I also took of the cylinder
head and cleaned that up and re-seated the valves. Does anyone know
what the carb needle valve settings should be? Also what does the Air
needle valve do and what is the setting for that?
Or any ideas on hy it won't run properly? It will start on the first
pull but then dies after about 5 to 10 seconds. If I open the choke,
it won't run at all. If I'm quick enough and manage to put it into
drive during the first 5 to 10 seconds then it picks up and runs for 30
seconds to a minute and cuts grass! The lawn is going to take a long
time to cut if I have to keep restarting it evey minute!! Any ideas??