Tachometer not going above 5k?

[Tola]

I think this is posted in the right section?

The tachometer on my '77 gs750 will only climb to about 5000 rpm, at that point it just bounces from 5k to 5500. Pulled it off the bike and I tested it with a piece of cable attached to a drill and it will climb smoothly to redline and stay steady at any rpm range. Do the cables wear out or could there be an issue with the gear drive for tach cable?

[Tola]

I'll update this so it may help someone else out in the future.

Problem is not fixed yet but I think it's come down to the cable.

Here's how to diagnose and rule out good components-

First I unhooked the speedo cable housing from the head,pulled cable, cable looked fine so reinstalled.

With a cordless drill with a flat head bit I was able to spin the cable in its housing from the bottom. RPM's climbed to 9000 smoothly and help at any RPM.

I checked the drive gear in the head which comes out but takes a good pull due to the o-ring. Looked good, minimal wear.

Put it all back together.... RPM's would not climb above 5k!!!

Spoke to an old school mechanic who thinks it's the cable and/or the bushing up inside the tach where cable enters. He's seen the bushings get pushed up and as the cable spins it may float fore and aft and loose contact. We'll see when new cable arrives.