adjustable voltage regulator

I added a volt meter to my KZ305. I found there are times when riding ,battery voltage goes as high as 15.5v. In hindsight, maybe ignorance is bliss. I may just get another KZ305 regulator and see how that works. But I remember long ago, my grandfather would adjust a screw in the regulator of his 56 Ford Fairlane before going on his annual American Legion convention trip. He said he liked to reduce the voltage when taking long trips. Are there adjustable regulators today?

Some early 70's bikes with single phase generators that have separate regulator and rectifier are adjustable (although after 45 years the adjusters are probably seized solid) combined reg/rec units aren't adjustable. I would suggest you check the accuracy of the voltmeter you have fitted and if it's correct you will probably need to replace your R/R before it boils the battery. What is factory spec for generator output for your specific bike ?

Generator output is 13.5A @ 8,000rpm 14V. Volt meter readings on bike is matching Fluke multimeter.
I took the bike out last night and got voltage readings as high as 16v on 55mph roads @6,000rpm.
I spent a few hours today cleaning and applying dielectric grease to all connections under seat, behind side covers, and in headlight bucket. Also, ground connections to frame and engine.
I went for the same ride tonight and the highest voltage I saw was 14.8V, and tended to stay around 14.5V. Idle was 13.2V @ 1,400rpm.
Problem solved.