B = Battery
A = Armature
F = Field

If the Field wire is shorted to ground, the generator voltage will increase without limit as the speed increases. Take the cover off that regulator and see if the points behind the F terminal are stuck together. Once they're free to move, decreasing the spring tension will lower the regulated voltage. That one's some type of off-the-wall aftermarket regulator- - - - -pitch it and get an original-equipment type would be the best choice.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!