Their could be a number of factors as to why he is behaving this way. It is hard to diagnose or give advice when you don't actually see or properly understand the situation. We only know what you are telling us, we then try and understand from what you are saying, what the horse is telling us. I do not believe the bit has anything to do with your problem. Nor do I think the saddle or any of your tack have to do with the situation, it seems like you know what you are doing in that category.
When correcting this behavior my question would be, are you being assertive? Some synonyms of the word assertive are confident, firm, or even aggressive. What I mean by this is when the horse tosses his head or acts out against what you ask him, what do you do? Do you take a step back and calm him down before asking for it again? Or do you get his feet moving or give a firm tug. This horse needs to be taught white and black, when he does what you ask the white is pure and comfortable. When he tosses his head (does he know this is wrong?) he needs to understand immediately that is something you don't like. You do this by being an assertive leader, confidently and aggressively getting him to understand you didn't approve of his actions. If you are working from the ground and he doesn't do what you are asking, and starts tossing his head. I would give a firm tug on the lead rope and get his feet moving. Get him to trot a few circles then ask him again to turn. If he tosses his head and pulls back, get after him!
He will learn the quickest this way, this horse apparently believes he can get away with things. From what I have read this is a matter of respect not of lightness in the mouth, it isn't that he is responding slowly to you asking for something with the bit. Instead he rebels, pulls back, or tosses his head, teach him that if he does this, it will be ultimately uncomfortable. Teaching correctly can be the greatest form of love.
Last edited by Toymanator; 04-02-2010 at 02:21 PM.