How do you know if you changed velocity? Larger ports tend to reduce velocity and will reduce flow as well if they are the wrong shape. A.G.Bell has a nice section in his book on 4 stroke performance that explains the different parts of a part and their relative shapes/sizes.
On the fuel side, you are almost right but slightly back to front. Fuel is mixed with air in a carb and the fuel is changed from fluid in the float bowl to small droplets as it emerges from the needle jet. By mixing air with the fuel in the so called "emulsion tube" the droplet sizes are reduced. Those droplets are not vaporized by a rough surface, but will separate out of the flow in a polished port. Fuel injection as the advantage of pressure. Where a carb relies on atmosphere./gravity/pressure differential to get the fuel moving, FI can operate at much higher pressure and potentially through small orifices all of which encourages smaller droplets which burn faster.
In the combustion chamber a polished surface will reduce heat transfer and the mixture temperature will potentially be higher leading to detonation in a worse case scenario. There are those who argue that a thin layer of carbon protects the heads even though it will raise the head temperature and reduce combustion temperature slightly. You could conduct your own experiments to see which variable has the greatest effect in your particular situation.
"More air only means more power" only when gas velocity is high and flow into the head is higher. With the same size valves and cams, porting is only useful to the degree to which flow is restricted. If a head already flows more than the motor needs, any further flow increase just results in lower velocity, less turbulence and slower combustion. The most critical area of a port is the 1/2 inch to an inch just before the seat.
One thing to avoid is directing the flow at the valve stem, the gas has to go around the valve to fill the combustion chamber and the easy thing to do is to open it's mouth behind the seat and that hurts flow.
Grab a copy of Bell and read all you can by Vizard and ignore most of what you read on the internet.
On the fuel side, you are almost right but slightly back to front. Fuel is mixed with air in a carb and the fuel is changed from fluid in the float bowl to small droplets as it emerges from the needle jet. By mixing air with the fuel in the so called "emulsion tube" the droplet sizes are reduced. Those droplets are not vaporized by a rough surface, but will separate out of the flow in a polished port. Fuel injection as the advantage of pressure. Where a carb relies on atmosphere./gravity/pressure differential to get the fuel moving, FI can operate at much higher pressure and potentially through small orifices all of which encourages smaller droplets which burn faster.
In the combustion chamber a polished surface will reduce heat transfer and the mixture temperature will potentially be higher leading to detonation in a worse case scenario. There are those who argue that a thin layer of carbon protects the heads even though it will raise the head temperature and reduce combustion temperature slightly. You could conduct your own experiments to see which variable has the greatest effect in your particular situation.
"More air only means more power" only when gas velocity is high and flow into the head is higher. With the same size valves and cams, porting is only useful to the degree to which flow is restricted. If a head already flows more than the motor needs, any further flow increase just results in lower velocity, less turbulence and slower combustion. The most critical area of a port is the 1/2 inch to an inch just before the seat.
One thing to avoid is directing the flow at the valve stem, the gas has to go around the valve to fill the combustion chamber and the easy thing to do is to open it's mouth behind the seat and that hurts flow.
Grab a copy of Bell and read all you can by Vizard and ignore most of what you read on the internet.