What would cause my tach needle to bounce?

If memory serves you have a nice original piece? You could still keep all the stock equipment and use a digital tac off the coils.
On my XS2, I had the tach apart when I refurbished the gauges. Everything was cleaned, everything is very solid feeling, cable is new and oiled, fittings are tight. The tach used to operate smoothly, then recently started bouncing in the upper RPM range. Now it bounces anywhere above idle. And I mean pretty big swings, for example if I was turning at 3500 rpm, the gauge would bounce from 3000 to 4000 RPM.

I’m not really anxious to open up that gauge again, but I’m trying to figure out the most likely suspect.

I have done a forum search and it usually came down to something was loose, but I’m not seeing anything that jumps out at me. Any ideas?

G'day B-O-B,

I used to repair these suckers and it seems to me that you
have not returned it as it should have been.

re-openit and make sure that the pointer (needle) is in the correct position .

May not be on the money but to me if it is bouncing then you need to open up again, sorry but is an internal problem for sure.

Good Luck,