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