Tachometer Erratic at High RPM

[knotscott]

When I rev into the higher RPM range, the tach on my "79 GS750E moves erratically, making it hard to know for sure what RPM I'm at. It sort of bounces back and forth a bit. It seems fine until I get past 7K. Anyone else ever experience this? Causes/fixes?

[koolaid_kid]

"Most" of the time it is the tach cable. Remove it (it goes from the head to the tach), remove the inner drive cable, and clean everything. Then lube the inner cable and re-install.
If it is too worn it may need to be replaced.

[tkent02]

Probably the cable, but if tht doesn' fix it you can also try shooting some spray grease between the part of the tach that spins with the cable and the threaded part that it spins in. You will probably have to take the tach off and turn it upside down to get it in there.

[Grimly]

Yep; bouncing speedo or tacho is usually (99%) cable related. Sometimes it's an indication it's on its way out, but normally it's early warning and a lube fixes it. However; I've found the GS tacho cables aren't really long-lived items - I don't think I ever had one that lasted more than 20 or 30K.

[JTGS850GL]

If none of the other options above cures the problem then it may be a dry tach assembly. I've had a couple that were not the cable and oil in the end did not fix it. I've had one tach that had seized and literally exploded internally. On the two that were salvageable I ended up having to disassemble the tach and lube it directly.

[tkent02]

Yep; bouncing speedo or tacho is usually (99%) cable related. Sometimes it's an indication it's on its way out, but normally it's early warning and a lube fixes it. However; I've found the GS tacho cables aren't really long-lived items - I don't think I ever had one that lasted more than 20 or 30K.

Had several around 100,000 miles without buying a cable.

[knotscott]

Thanks for the tips....will give them a try.

[allojohn]

When I rev into the higher RPM range, the tach on my "79 GS750E moves erratically, making it hard to know for sure what RPM I'm at. It sort of bounces back and forth a bit. It seems fine until I get past 7K. Anyone else ever experience this? Causes/fixes?

You need to get past 7K more often....it's just not used to being there .

[Grimly]

Had several around 100,000 miles without buying a cable.

What type were they?
I learned to avoid the listed ones with a kink on the outer end at the tacho, where it bends to clear the instrument housing - genuine stock, too, just a design flaw.
The inner cable usually fractures up around there.
Last ones I bought I rummaged around the dealer's stock and found other ones without the kink. They lasted fine.