Outboard carburetor nozzle/jet consumption?

Like Frosty said, changing to larger jets does not increase power, the jets are changed because other things have been done to increase power.

Smaller jets can make it run hot, resulting in holed pistons or seizing, larger jets make it run richer and dirtier, resulting in fouled plugs, carbon build up, broken rings and/or pistons.

This is one of the biggest misconceptions about outboards and increasing their HP.

 

Ok We have established that,

There 15's carb must be delivering more AIR AND FUEL. So in addition to the larger jets there is this diaphragm thingy on the larger carb (see pics), could this be what's delivering more air?

Take a look at the pictures, the 15 has these extra parts:
10 - DIAPHRAGM ASSY 1
9 -COVER, DIAPHRAGM
This is attached to a
34 - CHECK VALVE ASSY
15HP Carb

9.9 Carb


Boat Speed

 

No, to deliver more air the carb body needs to be different, the throat needs to be larger. I don't see a number for the carb body, is it listed someplace else?

I only mentioned the jets because its so common.

 

By George, I think you've got it!
that makes sense now, thanks.... there isn't a part number for the body alone, part 1 is the CARBURETOR ASSY, that's the hole damn carb... guess they don't let you just buy the body for a reason.
So I guess it's $218 for the entire carb and i have a 15HP
or $100 for the correct size prop for the 9.9

Anything else I might need to change? as I mentioned all other parts are the same, have gone through all of them in excel. According to the manuals, Also the same is : valve clearance, bore, stroke, displacement, plug gaps

 

Ign timing will be different.

 

Thanks guys, for all the advice, much appreciated.
I'm going to order the carb. I'll let you know how it turns out and I'll update the boat speed and propeller selection article with the results.