4HP to 5HP conversion

[H20]

OK I was thinking that while I am rebuilding the 4 hp maybe I could turn it into a 5 HP. According to the parts list on this site ALL engine parts are the same. I dont get it. Acording to YAMAHA's site they have different part numbers for piston, Crank cases, carb jets and some misc stuff.
So can I upgrade the 4 to a 5? It would be VERY nice if I could toss in some new carb bits and get more power for the inflatable for sure. Any help? I have model 4sj and was referancing parts for 1999 model's 4 and 5. 2 stroke.

got a lot of $ for 1 hp?

[H20]

I dont figure 5 or 10 bucks for new jets alot of money for a 25% increase do you? Depending on what you look at thats the only difference. That 1 HP might get both me and my wife on plane in the dink.

looks like a carb
probally a bigger diameter
call usa yamaha and ask