Re: 816 No Spark
The red hood tells me that is an 8000 series tractor. Gravely changed the color scheme from red with white hoods, and seat pans on the 800 series tractors to all red on the 8000 series tractors. Same tractors though. With the 16 (16.5) HP Onan twin, it would be an 8160.
Newer 8000 series tractors received the new style seat pans, and revised front grill surrounds. Your 1978 tractor still has the earlier 800 series grill surround.