I learned my lesson when buying a used engine. Always check out valve gaps, timing, etc,etc.

I picked up a used Saito 220. Figured I would give it a go without checking the settings. Well, after chasing after the spinner and prop a couple of times I pulled it apart and found the valves so far off it wasn't funny. Also found that during the violent backfires 4 teeth on the cam gear were stripped off.

After replacing the gear and adjusting the valves it runs like a top. But, the point is I now always check these things before firing it up.