Can you convert a 9.9 HP to a 15 HP?

[wncmtns1]

I have a 1998 9.9, and I could use a little more HP. I know that the 9.9 and the 15 both use the same block, etc., so with different jets could this conversion be made? Would anything else be needed? Anyone guess at the cost to do this?

[rodbolt17]

check the two on the parts catalog for the 9.9 carb,15 carb,15 reed assy and the 9.9 reed assy.
best I recall its only the reed assy.

[wncmtns1]

I believe you're right. The carb is the same, and actually every spec is the same and the only difference is a much wider opening in the reed assembly (reed stops allowing for more opening, and I would assume that just means the engine is getting more air and fuel). slightly more RPM (200), and a slightly larger prop (1/2 inch). Looks like the 9.9 is a 15 with a choke hold on the intake. This should be a fairly easy conversion.

After a little more research, I'm not sure what prop to go with. I am currently running the OEM 9.25x9, and I think that I will need more pitch, something like 9.25x11. Any thoughts?

[rodbolt17]

actually, the 9.9 has a two leaf reed assy and the 15 a 3 leaf.

[wncmtns1]

I pulled mine out of the 9.9 when I rebuilt the carb in February, and it had a 3 leaf assembly. It was very clean so I put it back in, but definitely 3 leaf, with 3 limiters on each side. Maybe a change since they had several different models-something like 6 or 7 in 1997 and 1998. What are your thoughts on the prop?