Johnson 15hp carby wanted

[ozengines]

Hi all, I have just bought a 12 foot Tinny with a 9.9 Johnson motor. I want to upgrade to 15hp as I have read this can be done.
So, I am after a 15hp carburettor. Is there anything else I need to complete the upgrade, I have bought the 15hp exhaust megaphone.
The boat does not quite get up on the plane with the 9.9hp.
Model number: J10RLCNS 1982 MODEL Serial Number: A694029
My 9.9 carby number is OMC 0389914 : Replaced By 0395509.
The 15hp parts list shows the same carby. So, is there a difference or are they re-jetted ?? I was under the opinion that the 15hp had a larger throat and jet, or have I been mislead ?

Peter, Australia

[Rebel Sympathy]

This is one of the few rumored hp upgrades that seems to work. I think you are good to go.

For the rest of us...... don't think you are going to re-jet a carb, or swap a carb and make a 25 into a 35. It won't work. Port timing is different as well as manifold and carb size.

[ozengines]

So does anyone know if it is only jet change, somewhere I read that you need the 15hp exhaust megaphone to get the full 15hp.
Really would love to know if this upgrade is feasible before I actually commit to buying the exhaust.