What the other guys said. Just don't run it too rich and cold. If you can just barely hold a finger on the head with a good smoke stream, that's about right for wide open run-in. If you hear the engine has a funny click-ity sound at idle, you know it's still tight and it's not at a good speed to let run at. Run it in some more, it will go away. On new or tight pinch engines, cold running and/or low speeds are hard on con rods and other parts and only extend the run-in process.