Back in 1978, an 80 hp Merc had compression in the 180psi range, so a high octane fuel is required. Basicly, if your readings are at least in the 110 - 120 psi range, and no more than 10 - 15 psi variance between the highest and lowest reading, you should be okay.
1978 80 Mercury Outboard IDLE ADJUSTMENT
1978
A 50 hp Mercury outboard, serial number 5111678, is a 1978 year model.
1978
The 1978 model, 9.8 hp Mercury outboard, requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
A 9.8 hp Mercury outboard, serial number 5208019 would be a 1978 year model.
Hello.... it appears your outboard is a 1978.
The 1978 model, 115 hp Mercury outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
A 90 hp Mercury, serial number 4849632, is a 1978 year model outboard.
No as all the inline 6 cylinder motors are a 2:1 ration and all the small inline 4 cylinder are 2:3:1 ratio
The 1978 model, 75 hp Mercury outboard, requires a 50:1 ratio, roughly one pint of 2 cycle oil, to six gallons of fuel.
A 9.8 hp Mercury outboard, serial number 5123082, would be a 1978 year model.