If your bearings have grit they always will until you take off the shields and completely clean them. Then they will be clean for about 3 track sessions.
Get new bearings with rubber seals and you’ll never have grit again. New bearings don’t need break in. The grease is all through the bearing making it stiff but the grease will move when the bearing gets warm and free up first time you’re on track. Using light oil will cause your bearing to chatter and bind so, get bearings with rubber seals, put them in as is.
If you just want the axle to spin forever on the kart stand clean out all the grease and spray with wd40 but, grease is faster on the track.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience