I recently paid way to much for a Kirby Classic 1-CR in pretty bad shape. I oiled the front bearing to stop the terrible squeaks, and shortly after that, I powered it up to see how it ran. When I powered it on I heard A very brief electrical jolt sound followed by a low buzz, hardly audible for the machine running. The whole time I was thinking to myself "For the love of GOD don't arc." So I look down in the vent holes only to find the Blue Fireworks Spectacular off the brushes. What does this machine need to stop arcing?
Your first mistake was to oil the bearings, the bearings on your Kirby Classic are packed with grease, when you put oil in them you are actually breaking down the grease and defeating the purpose. I would take the 3 screws off the motor shell and check the condition of both the carbon brushes and the commutator on the armature. Remove the brushes, check the length of the carbon, it should be about 3/4" long, also make sure the sides of the brushes don't have any grooves in them and finally make sure the spring is not discolored from excessive heat. Check the copper segments on the commutator, make sure the spaces are even and none of them are discolored. If you can, post a picture of both the brushes and the commutator and I will try to help you get it going again.