You can check the spark quality using a spare plug, if you hear a nice snap with every spark and they are blue then all is well, if it's a little weak or yellowish it isn't. The spark should jump around 1 inch easily in normal air and still make a spark at the plug.
What grade os plugs are you using? take one out and chack the condition after it's been idling, it may be fowling up.
Are you sure the carbs are set-up properly?
Is it choking on the crank ventilation, or is a breather blocked.
How quickly does the stall occur?