Im wondering why when I go to solve the camera in a tracked scene it defaults to being set to having a focal length of 24. If I have the focal length above or below 24 before doing the solve it sets it back to 24, but I would like it to stay at the focal length I have set before the camera solve.
Motion tracking Solver does not automatically applies the settings of the Solved camera into your scene's camera unless you press Setup Tracking Scene (Movie Clip Editor Window, in the Solve Tab).
Blender's default camera has 24mm so I guess you are not using this feature. If not, you may apply the Camera Solver Constraint manually and then change the Camera properties too.