It sounds almost like he's experiencing pain from the bit. Have you had his teeth checked by a vet? Not just floated, but checked thoroughly for sharp teeth, etc.
And, of course, re-check placement of the bit in his mouth. I'm not that familiar with bit type names to know exactly what kind of bit you are using.
My arab always reached for the bit when I was bridling him. One day he quit doing that and I realized his bridle was much more difficult to put on him. I talked with my husband and found out he had "adjusted" the horse's bridle fit. Well, I readjusted it back and it took a year before he began to reach for the bit again. He expected discomfort and wasn't going to volunteer for the bit until he was sure it was comfortable again.
It's hard to know what is meant by the previous owner's statement about the bit "not doing the job." We use an egg butt snaffle to start our horses.
How was he ridden by the previous owner? Is the horse expecting pain or heavy hands when you start out? Is he reacting to history rather than present handling? Is this a new problem or an ingrained habit? How long have you had the horse?
Occasionally I round pen my Arab for about 10 minutes before going on a trail ride. He tends to chew on the bit when he gets stressed and antsy. He's a great trail horse, but the few minutes of round penning seems to calm and focus him.
Possibly you need to take a few steps backwards and start at a lower level of training, provided you are sure his teeth and tack are good.
Maybe go back to groundwork with the bare essentials re: tack, then work up to lounging with full tack, including bridle and bit. See how he reacts to various pieces of tack while you are working him from the ground and can better observe him.
Sometimes we get to thinking only about hardware and changing that hardware to "fix" a problem, when what is needed is to go back in training and gradually work back up. Take it slow, and observe him closely.
One more thought. I thought I was riding my arab with a saddle that fit him well. Unfortunately, he had grown quite a bit over the winter, and I didn't realize the saddle was bothering him. He was head tossing and not nearly as calm as he had been. The subtle weight shift when we changed gaits caused the saddle to pinch at the withers. When I changed to a different saddle, he settled down to his old self. So, you may have to look beyond the bit.
Good luck!
> My horse Frisco has a very
> sensitive mouth. He plays with the
> bit when we stop and when we trot
> he throws his heaad up when he
> starts to trot like a maniac! I
> really don't know what to do... I
> ride with extremely soft hands.
> I'm riding him in a
> kimberwicksnaffle cross, the
> previous owner said a huge snaffle
> wasn't doing the job... HELP!
