'96 Fatboy and the speedo needle 'flutters'. Always had the issue when >100 mph, but it's now started doing it over 60 mph. Once I hit about 60 mph now the needle will flutter between 55 and 70 on a bad day or between 60 and 65 on a good day. By 70 mph it's between 65 and 80. Have to use a phone with Sat. Nav. for a more accurate speed. It's good as gold up to 50 mph, Has anyone else seen this sort of thing?

 

Have you got a speedo cable going to the front wheel?

Was a common thig on older bikes and cars for that matter. Start there
Lube the cable if you can otherwise replace

WP

 

Pull the speed sensor on the transmission and clean it, it's magnetic and could collect wear particles from the trans oil.

 

I replaced my original speedo this summer because the odometer was broken. The after market replacement did this. Ran great up until about 600 miles then it started fluttering. Started with a small range of fluctuation that increased with each ride. At around 800 miles it was bouncing around +/- 20 mph then the needle just started spinning full circles at a very high rate of speed. The needle snapped off after about 10 min of that. The center "wheel" is still spinning full circles and looks like it's coming off sometime soon. Odometer appears to still be running correct but I have not verified against gps or a mapped route. Not going to mess with it until winter and I have no idea what caused it. Mine is a 87' Softail with a cable to the front wheel.

 

What if AC voltage was getting past the diodes in the regulator, could that cause something like that?
You could run it with the regulator unplugged for a quick test.

 

I believe that a 1996 Harley Fatboy would have an electronic speedometer but unsure.
The odometer would be an LCD screen instead of the numbered wheels that spin to indicate distance traveled if electronic.
You state "Always had the issue when >100 mph".
Since you state "always" does that mean you have owned the bike since 1996 and you never had the bike into a dealer for warranty work??
If it is an electronic speedometer:
If the motorcycle is operating correctly then i would take a look at voltage at battery posts with a digital voltage meter.
Basically looking for an over voltage or loss of voltage situation as you increase RPM. Review the charging system.
A voltage spike or unsteady voltage could cause an electronic speedometer to function incorrectly.
If somebody re-routed speed sensor wire really close to a spark plug wire then signal interference could be possible.
I would also remove the speed sensor and review for metal filings too.
Their is a possibility that speedometer itself could be defective but a test would rule that out.
If it is a cable speedometer then the speedometer drive at front wheel, cable or speedometer requires review.