I've heard alot of people talk about converting their 9.9 hp motors into 15's and such. I know they aren't joking around either because their boats are way faster than my boat. I'm talking 2 big guys in a boat (200+ lbs) just completely smoking my brother and I (100lbs each). Maybe they can only do it for 2 stroke motors or something, I was just wondering how you do it. Not really worried about it, just want to know if anyone here has done it, or has heard of it.

BTW this lake we fish tournaments at is 9.9hp limit and pretty much everyone of the boats is over than HP.

I have converted an old 85hp into a 115hp and all I had to do was put a bigger carburetor on it (or basically make the engine suck up more fuel).  I would imagine that it be the same for converting a 9.9 into a 15.

T-Bone

T-Bone is right. Just change out the carburetor.

Yeah I was reading on some other websites that all you have to do is change out the carb and sometimes the main jet.

is it as simple as going to marine mechanic, and saying you want a bigger carb put in, and they will do it?

on most its just new carbs( or just jets) and  new exhaust tube

it depends on what make of motor