Re: How does this work?
OK, if and when you do remove that brass ring, know that there is a right and wrong side to the aluminum ring, the flat side should contact the underside of the brass ring. If you reverse it, the armature plate will bind and you'll go nuts trying to sort it out, anyway read on
Here's a post from our good friend J. Reeves that explains the 'fix' for a wobbly armature plate. His reply helps a fella with a fix for a motor that fires on only one cylinder, but the fix applies to your situation too...
"That problem is usually caused by one of two things (or both) assuming that the points, condenser, and coil are okay.The first is that one of the spark plug wires has chaffed through which allows it to ground out as the armature plate turns.The second is that too much rocking type motion exists in the seating of the armature plate (the plate the coils etc are attached to). The solution to this problem follows.
(Magneto Armature Plate)
If the armature plate has a a loose fitting, wobbling motion (the plate that the points, coils etc are attached to), it is usually caused by a slightly worn support ring. This allows the point setting to change erratically as the armature plate turns. The cure is to remove the armature plate so that the support which is attached to the powerhead with 4 screws is visible. Then, with a screwdriver and hammer, or some tool of your choosing, and looking straight down at the support ring, make an indentation at what would be called the 12, 3, 6, and 9 O'clock positions. Install the armature plate and check for a smooth turning wobble free movement.You may need to do that procedure a few times to obtain the proper fit (not too tight, not too loose), but it's worth the effort."
Btw, I have use this procedure with great success but a few words of caution are in order. The idea here is to make small dents in the brass ring at 12-3-6-9 o'clock positions with a screwdriver blade. The aluminum ring underneath will now 'ride' on those 4 locations reducing the wobble. Here's the caution part, don't get nuts with the hammer. It only takes a slight bit of deformation at each location to get the desired result. If you did overdo it, you'd remove the brass ring and flip it over and tap it back flush..you get the idea.