Laser settings in GRBL

I have the 6550 laser and cannot figure out the settings in laser grbl to do any burning, one time it will burn ok but if i change any of the settings it wont burn at all. please help

What settings are you changing?

Can you provide a little more info - what sort of speed and power are you using, has the laser been set to the proper height for focus, etc.

This will help us help you - need to know what we’re working with.