Re: High Altitude
You will notice the difference in power, kind of depends on the engine and how it reacts to altitude. I've had a couple outboards from 5000-9000', one wouldn't run worth a cr@p above 6000', the other one would run, but seriously down on power. My I/O runs OK, but has a noticeable lack of power. All of those were without tuning for altitude.
With my 7.5 HP Gamefisher (Force), jetting down the carb helped, but not enough for me to go through the hassle of jetting it down for a 1 day trip, I'll do it if I'm up there for a couple days though. On my 140HP Mercruiser, I change jets and prop to get the boat on plane, without that it struggles really bad to get on plane, idles OK though.
Rule of thumb, for every 1000' you loose 3% HP, so up at Tahoe you are down about 18%.
I would try a lower pitch prop first, easier to change back and forth.
