My brother learned a ton of math working on the equipment he loved--he never wanted to learn math for the sake of learning it, even though he had a talent for it. He only wanted to learn it if it helped him with his projects or he could see that it would be useful in future projects. It seems like science could be the same motivator for your son.
Math, as it is usually taught, is separated from its real-world applications and larger world ramifications. I think that is why many people don't think they are good at it. Many people who don't think they are good at it use it regulary in cooking, crafts, carpentry, navigation, etc. I bet if he could see how it helped him understand bombs, weapons, science etc, you might see him grab onto it again. Just stay away from math for math's sake.
