Im not sure where to find info on the net. Buy a factory manual or a clymer manual. They do go into some theory.
Jetting is about getting the right air to fuel ratio or mixture. To much air, and it will run lean. To much fuel and it will run rich.
If it is lean, it will run hot, sputter\starve for gas, it can detonate. Deffinitely not good.
If it is rich, it will have a lazy throttle response, foul spark plugs, and generally be gutless.
So on a perfect day, you can achieve good jetting results. Jetting can change upon the weather.
A cold day, and raining outside, will cause the jetting to be lean. You need richer(bigger) jets.
A hot day and or humid day will make the jetting rich. You need leaner(smaller)jets.
Elevation(higher) will make the bike run rich. you need to jet leaner. Just remember to change the jetting back before you ride at lower elevations again.
Exhaust upgrades and air box modifications will change jetting. So will porting and cams.
Its really a science, and can be hit and miss. Its a good idea to have a good selection of different sizes available, for impromptu tuning in the field.
I think ive rattled on long enough.