sounds to me like you have an air leak involving your intake manifold, but not a very big one. when the engine is cold, the mixture's ok, but when it gets hot, the overall condition is too lean, which can cause racing/poor idle. you're partly compensating with the fairly rich main jet (though that's not crazy-rich, incidentally, depending on where you are). you should idle the engine, and then spray carb cleaner around the intake to test this theory, being careful not to get any carb cleaner into the intake tract itself. if the engine races, then you have a leak where you sprayed.