Alcohol has a higher latent heat of vaporisation than hydrocrabons. It lowers you carburetor temperature which causes the incoming air to become denser and thus leans-off the mixture. If you get an increase in revs, it means you were previously jetted slightly too rich. If you get a miss, it means you are not jetted rich enough. If you don't change your jetting when using normal petrol, but either slightly raise the comp. ratio or increase the ignition advance, you would get the same effect as when you lean-off the jetting by using alcohol in your fuel.
You should always jet to suit the fuel you are using. It should not matter what the fuel might be. It should usually only be a matter of raising or lowering the needles, one notch.
The calorific values of all the fuels you buy from the pump, should all be very similar. The amount of ethanol is almost nerglible in that context.
When you buy petrol from a pump, it is all garbage anyway. I suggest the reason ELF fuel became commonly used for racing, is it provides consistency, so is easier to tune,
