For a "low tech" engine like a motorcycle it probably isn't really challenging, but here is the quick rundown...
Alcohol requires a different air/fuel mixture ratio. A gas engine mixes 14.7 parts air with 1 part fuel, but for Ethyl alcohol (corn mash white lightin) you need more like 9 to 1 ratio. If you have mixture adjustment screws you may be able to adjust it richer, or else you may have to take apart the carburetor and rebuild it with "richer jets". There are probably some other important reasons you need to rebuild the carb... because if you plan to run on 100% alcohol, this will quickly destroy any RUBBER components in your fuel system. If you have a rubber fuel line it needs to be replaced with braided steel line. Any rubber bits in the carburetor need to be replaced with "suitable material" compatible with alcohol.
On the other hand, Gasoline/Alcohol mixtures with around 10% alcohol work pretty much OK in unmodified engines, and if you look at the gas pump some stations in some areas mix in a bit of alcohol and they print "may contain up to 10% ethyl alcohol" on the pump. And fact is you will get lower MPG with this fuel, but it is slightly better for emissions for some months of the year, I think mainly the WINTER months.
And the reason why it is a bad idea to run Gasohol in the SUMMER is that alcohol has a lower vapor point... which means that your fuel evaporates in ambient heat more easily, so then your vehicle gets really horrible mileage.
This link has some info on how alcohol burns different from gas and how this affects conversions...
http://www.ext.colostate.edu/Pubs/farmmgt/05010.html