Thank you so much.You are asking a question that is answered in the manual.
It says the wide part of the brush should be a minimum 1/8” length.
Replace the springs if they’re rusty or not pushing the brushes out.
Don’t replace the brushes if they’re not worn out. There are soft ones on sale nowadays, that cover the slip ring with carbon and cause misfiring.
There are soft ones on sale nowadays, that cover the slip ring with carbon and cause misfiring.
If the surface of the slip ring conducts, then a spark will occur at the plug which is not under compression.
This is a very helpful thread as I am looking at a 650 with exactly that problem.