Brightspark Magnetos

With the earth brush(es) now replaced, measure the resistance between the back-plate of the contact breaker assembly and the main body of the magneto.

The reading should be less than 30 ohms.

If higher than that, investigate. For example:

• Check as best you can that the brush is actually making contact with the track on which it runs.

• In the case of a main-body earth brush, try moistening a cotton bud with petrol, and poke it through the hole for the earth brush to clean the track while rotating the armature, but IMPORTANTLY before doing that temporarily remove or disable the contact breaker to reduce the risk of electric shock and fire.