http://www.johnnycoolguy.com/JCGR/ma..._break-in.html

One thing I do different is run it for more then 2-3 minutes at a time. You cant get temps up to 200 and maintain that temp for 2-3 minutes if you try to ONLY run it for 2-3 minutes at a time. I suggest you run it a half tank to a full tank and wrap the head with a sock or something that will hold in heat. This will allow it to bring temps up faster. And also you will be able to run the engine richer at optimal temps (around 200 degrees) which will help to flush the small particals that accur when breakin in the engine.