Hmmm. Where to start?
OK... z is the default key for zoom toggle, not i. Did you change this?
The default mapping for i is elevator trim down. Did you change this also?
The square bracket keys ([ and ]) zoom in and out after the z key is toggled.
Why don't you reset the zoom toggle back to the z key and use it? Also, reset elevator trim back to the i key.
Vehicles are mapped separately as Mode 2. After you've reset everything back to the original settings, go to Options Controls, Map Controllers and copy Mode 1 to Mode 2. Make sure you have selected Mode 2 in the top drop down menu and set your change gear up and down, etc.
Select the box to automatically select Mode 2 for gvs.
Also, when you are in any other position other than the F1 (cockpit) view in bombers, the level of zoom when you toggle z is dependent on the zoom in the F1 view. So, set a small zoom with [ and ] keys while in F1 view, then you can adjust more while in the F6, gunner or other outside views