Improving my bowling score and average...?

I have about a 160 average and shoot over 200 about 1 in 4 games. I know I have a good ball and and a great approach. I'm a "down-and-in" bowler, hitting the same line every time and I'm pretty consistent. I hit the pocket or close to it every time, but I'm not getting the strikes; I have a brand new ball (Black Widow Bite, 15lbs.) and everything seems to be right but I just can't seem to knock 'em out. Any advice??