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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.
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How do you adjust the idle on a 80 hp Mercury Outboard engine?
1978 80 Mercury Outboard IDLE ADJUSTMENT
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1978
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