tryin to break in new engine, ruff idle

If you have flames during startup your cam or ignition is out of time. Have you put on a vacuum gauge? Are you 180 out on the dist? Recheck ignition timing - dist shaft slot should be facing forward and aft @ #1 tdc. Did you swap #5 & 7 plug wires by accident? It's a common mistake. Check your plug condition and find the dead cylinder. Check cam timing.