Marlin Z Axis feedrate

I use Marlin with RAMPS and Arduino 2560.
When I change z STEPS_PER_UNIT, no matter how small the change, z axis zero search feedrate became so fast that sometime it didn’t recognize the z endstop.
#define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,200*8/3,760*1.1}
I appreciate any suggestions.
Tony

You are changing the wrong value.
The value you are changing is the number of steps per mm. Which will cause your z lengths to be compresed or elongated if not set right.

You want to change
#define HOMING_FEEDRATE {50*60, 50*60, 4*60, 0}

Thank you so much for your help! It works now