To clarify what I believe is correct, if during your run up you raise power to 1700 rpm and do your mag check, turn to left mag good drop, back to both, then right mag and you get a bad drop or the engine runs rough. First thing you do is leave it on that mag so the right mag, then you lean the mixture as far out as you can get without engine quitting and leave it like that for a few seconds to get engine good and hot to burn off the carbon, then full rich and turn key back to both and then try the mag again. If this is wrong please clarify the correct procedure. Thank you!