{HEAD ~ A pair} of centrifugal governor are combined in {TAIL ~ an unit} for providing a compound spark advance characteristics 
are combined in
{ HEAD ~ A pair } of centrifugal governor are combined in { TAIL ~ an unit } for providing a compound spark advance characteristics
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH