Starts and then dies

Heres what happened, it ran fine for 20 min on break-in, and again for 10min to adjust the valves. After adj the valves, I started to tune (timing/idle/float level/idle mix) at which point it just died like I turned it off. Trying to restart it gave the same symptoms (stat/die) until the point where I had no spark (verified by remotely turning it over with the spark plug 40 thou from the manifold bolt).*