My unit is around 8 years old and only used for Winter power outages. It worked great last fall. Last week I started it for pre winter testing. It started and runs great but not it does not generate full power. When I discovered it would not light my drop light I tested the output at the receptacles and get only 4.2 Volts on each plug. I did check the electrical connections and the brushes. All were tight and clean, just like brand new. Any ideas what the problem could be?

Needs to be flashed , take it to a dealer and they should be able to do this.