I came across this video and it's quite revealing about how a carburetor works -- from the inside of the cylinder!
If you look carefully at the intake valve during the intake cycle, you'll see droplets of fuel spattering on the top of the valve head in addition to the cloud of mist being pulled into the cylinder.
The fact that you can see mist and droplets on the intake side demonstrates that carburetors don't 'evaporate' the fuel but rather induce a spray into the airstream and the evaporation takes place in the cylinder itself. (Liquid gasoline doesn't burn.)
The fuel evaporation is the product of the mist absorbing heat (heat of evaporation) from the cylinder and explains why you loose more power from a rich mixture than a lean one -- excess fuel causes excess cooling, slower evaporation and incomplete combustion.
The spray is actually fine droplets of fuel suspended in moving air and is produced by the 'foam' (fuel/air emulsion) in the carburetor passages being sucked into the air stream where the foam breaks up.
It's also interesting to see the relative intake velocity of the intake stroke. When the cylinder draw is maximum you see the mist form around the intake valve.
Pretty neat, huh?
Jim
