I've recently finished building a new cnc machine that's capable of going much faster than my old one. The motors have been tuned and everything seems to be running smooth. HOWEVER, when i load a g-code Mach3 seems to change the feed rate and units/min, causing the machine to crash if i run the program.

I've checked the g-code, and nothing is wrong with it. When i manually change the feed rate, the units/min stay the same when i move the axis. If i close the g-code, the feed rate still remains changed and the only way to reset it is by closing and reopening the program.

If what i'm saying is confusing, let me provide an example: My motors are calibrated to run at 50 inches/min. When i first open Mach3, and of course press reset, i can press the arrow keys and the machine moves accordingly. When doing so, the units/min go to 50 inches/min, while the feed rate remains at 6.00 inches/min (its the default setting for some reason). The moment i load any g-code, the feed rate drops to 0.24 inch/min, and when jogging the machine, the units/min only go to 2.02 inches/min. If i manually change the feed rate, it of course changes, but still the units/min when jogging do not change.

I did create a new Mach3 machine profile for this thing, since I'm still using the old mill to do metalwork. The old mill uses the generic Mach3mill profile, while the router uses a new one i named Router.

Does anyone know what is going on with this program and what i can do to fix it?

Your g-code probably has a feedrate in it, something like F0.24.