I worked at a GM garage when I was a kid and the owners occasionally put a can of GM's "combustion chamber conditioner" through an older car's engine. Part of the contents would be slowly poured through the carbueretor and then the engine would be stalled with the rest of the can. That would be left to sit for a few hours. When restarted, they would smoke like crazy. We considered a lot of smoke a good sign. It was really impressive anyway.