2nd photo of tach innards

[old smokey]

Here's another photo of the tach. Trying to find why the gage needle is jumping way high.

[Toystoretom]

I wonder if there is some rust inside of the cups that is causing friction between the two. I see some rust spots on the outside. I don't suppose there is any way to take this apart without ruining it.

Maybe you could do the rust removal thing I saw on here for gas tanks by using a sacrificial rod and washing soda with an electric current. But then again I drink a lot...... 

[old smokey]

I was wondering about rust in there. I did use some compressed air but don't know if it helped any. And then some oil on the spinning shaft beneath the cup assembly. More experimenting required.

[Toystoretom]

Maybe we are not thinking about the right test on this thing. GTR's would probably rev up to 6, 7 or 8 grand normally? What if you were to put your tach innards in a vice, hook a clutch cable up to it, and then power the clutch cable with something like an electric drill and see if those cups play nice together. This would assume that the clutch cable you are using is OK. If you had an old cable you could just use the inside drive part of it or make something that might work so you could take the cable part of it out of the equation.

If the cups are rubbing due to rust maybe you could put some abrasive in there like glass beads from a bead blaster or some very fine white sand and spin the thing for awhile with the above cable and drill thing and wear the rust out of there. A little compressed air would clear the abrasive out and then hit it with some brake cleaner to wash out the rest.

Like I said... I drink a lot 

[OldSwartout]

If the cups are rubbing due to rust maybe you could put some abrasive in there like glass beads from a bead blaster or some very fine white sand and spin the thing for awhile with the above cable and drill thing and wear the rust out of there. A little compressed air would clear the abrasive out and then hit it with some brake cleaner to wash out the rest.

That seems like a good idea to me, but be careful not to put anything between the cup and plate that will cause too much drag, nor anything magnetic (it will not come out).  Too much drag and you'll push the tach needle/shaft/spring beyond their limits and cause permanent damage.  Voice of experience here (car speedo).

[old smokey]

I took the GTR out yesterday afternoon to test the new battery to see if it was charging. On the plus side it's charging great, and I discovered that the head light problem was really only in the high\low switch. It's gummy and just needs to be moved more. I'm hoping to find some spray contact cleaner to help that. Richard recommended a battery for a 72 Honda SL 350. The local used bike shop got one for me for $26. Fits perfect.
The down side is my 5 mile trip was too much for the tach. I checked it half way around the block and the needle was broken off the shaft. 
One thing off the list and another added.