The problem isn't so much the lead from the info provided, it is the lack of cylinder pressure. Higher octane fuel needs more cylinder pressure to burn correctly, and will carbon up an engine, lead or no lead. We see this in the auto industry with consumers who use premium fuel in cars with lower compression ratings. They build up carbon bad, and eventually come in with all sorts of issues. Unless you are running enough timing, and/or compression, it will carbon the engine up every time. Lead may enhance the issue, as it was a lubricant for the valves as well as an octane booster.