Re: Johnson 70 hp vs Mariner 60 hp
It's also possible that the 90s 60hp might be very comparable in actual power to the 70s 70 hp. I think the 70's engine had horsepower rated at the head while the 90's engine is rated at the prop.
One question I would ask is - are you happy with the power you have now? What's the boat rated for? Because, if you're going to the effort of making the engine swap, might as well remedy any power issues you might have rather than just continuing on at the same level just to get power trim.
I've found power trim to be very helpful especially with dragging skiers, etc. If the 90s engine is clean and I had confidence it's a good one, and I think the HP would be good, I'd make the swap personally (assuming I thought it was worth the money it would cost). I wouldn't however expect to see a lot of change in fuel usage controlling for usage (cruise, wot, pulling things, etc) because both are carbureted and will likely have similar HP. Maybe some, but I wouldn't expect it to be meaningful.
