A high voltage form the regulator usually means that it's not getting either a good ground, or there's some corrosion interfering with it. If there's extra resistance in the system somewhere, the sensors in the regulator get a false reading, and it tries to compensate for it. It really throws your voltage off.
If the regulator is regulating 18V, then the components in it are likely to be okay. It's just having some trouble reading what the bike has, so it's doing the wrong thing.
Currently Running Stable:
2010 Honda NT700V
1986 Shadow 700
1986 Honda Trail 110 (Postie Bike)
1987 Honda Rebel 450
1973 Honda Mini Trail 50