You may have a dead/dying battery. What is your battery voltage at rest? With the battery hooked up and the bike at fast idle, what voltage do you measure at the battery terminals? Do you have a battery charger/tender? Hook it up and charge it at no more than 2 amps for 6 hours or so and see what happens then, and what happens to the battery voltage at fast idle.
How old is this battery and how much do you ride the bike?
It's more likely your battery is dying than your voltage regulator is bad.