Heat of combustion is what makes plugs look toasty brown ( normal ) and if a cylinder runs " cool " Plugs will be oily and black.-----A compression test is step #1 in trouble shooting.
Not much difference in them from one year to the next.----Simple carburetors , simple fuel pumps and a simple magneto.-----What is the motor doing / not doing ?-----If no spark then cleaning breaker points and setting them at 0.010" might help.
Have a pair of 1982 model 235 HP.----Yes they are thirsty.----You can work on them yourself.-----If you only use the boat on occasion there is nothing wrong with fuel consumption issues.----Hard to justify a new 200 HP motor so you can save $400 / year on fuel.
Some will argue-----These motors are nearly world famous for broken piston rings.----With 105 PSI on my tester the motor would be coming apart I think.-----Easy to inspect pistons / ring via the 4 wee bypass covers on the side of the block.
Sorry-----But the top carburetor only feeds the top cylinder !!-----Your motor is in fact 2 separate engines ( crankcases ) and there is a need to understand the concept !
Linkages do not go out of adjustment on these. !!----Sounds like you just need to revisit your carburetor work.----Perhaps a high speed jet ( orifice plug ) is plugged !
