What elevation and is the boat always going to be at that elevation?
- If always at high elevation, swapping jets AND a lower pitch prop would be appropriate.
- If temporarily using the boat at high elevation, swapping jets may not be the best solution since the jets would be changed back before running at low elevation again (lots of work). I'd just use a lower pitch prop for the short time at altitude.
If the outboard is run at low elevation with the high altitude jet(s), you could burn up the outboard, melted piston(s)...
I make trips to high altitude, but mainly use the boats at low altitude. In my little boat, I just swap props, 15 minutes and done. My big boat gets everything (jets, timing, prop) before heading to high altitude since it makes a HUGE difference, but that all has to be reversed before running at low altitude again. Lots of work....