Thanks Deejay. I notice those engines seem to be very late vertical-pull types, which I think means mid 1980s. Since both black and orange were running at that time, my guess would be that Briggs was allowing mower manufacturers to specify colour as an option when ordering batches of engines. This means it would have been controlled by the Type and Trim section of the engine specification. Hence there might have been more than 3 colours by then (black, orange, yellow, and maybe others). However that is a guess at the moment. Members with rainbow coloured original engines might be able to help us clarify what actually went on.
