You can find it here along with other diagrams and parts for the Gnat.
file:///Users/spc71/Desktop/Marine%20Parts%20Plus%20Mercury%20Serial%2040%204%20GNAT%202%20CYL%2074059%20472-6.html
A 9.8 hp Mercury outboard, serial number 4387693, is a 1976 year model. The carburetor used on the 15 hp model, is of a completely different design, and will not interchange with the 9.8 (110) model.
A 65 hp Mercury outboard, serial number 4574019, is a 1976 year model.
1976
A 65 hp Mercury outboard, SN 6315551 would be a 1976 year model.
50:1
There is no gap to set on most '76 Mercs Even if there were there is no clear way to answer the question since there are at least a dozen different models made by Mercury in 1976
The serial number OC121590 indicates that your Mercury 45 HP Classic Fifty outboard motor was likely manufactured in 1976. Mercury outboard motors typically use a coding system where the letters and numbers in the serial number correspond to the year of production. For more precise information, you can consult a Mercury outboard motor reference guide or contact a Mercury dealer.
The Mercury outboard motor with the serial number 6105283 is a 4.5 horsepower model manufactured in 1976. Mercury typically uses a serial number system that allows for the identification of the year of production, and the first two digits of the serial number often indicate the year. In this case, the "61" suggests it was made in 1976.
Mercury outboards manufactured in 1976 require a 50:1 ratio, roughly one pint of 2 cycle oil, to six gallons of fuel.
The 1976 year model, (ser.#4420321), 4.5hp Mercury outboard, requires a 50:1 fuel, to 2 cycle oil ratio. Mixing one pint of oil, to six gallons of fuel, will be a good mix.
The serial number for a 1976 Mercury Thunderbolt Ignition 850 outboard motor can typically be found on the engine's mounting bracket or the transom bracket. Each motor has a unique serial number that identifies its manufacturing details and production year. If you need the specific serial number for your outboard, it's best to check the physical motor itself or refer to any documentation you have for it.
10R76R is a 1976 model, 9.9 hp Johnson outboard.