Tach not working

hey guys, i got my bike running today (thanks only to the members on this site). it's a great stress relief hearing it run as i thought i might have a paper weight. Anyways, now that i've got it started i see the tach isn't working. i followed the wire to that huge bundle of wires in the headlight area and it appears to be okay.

where would i start looking to find the problem? Is it common for the tach to go bad, or would it likely be the wiring unattached somewhere?

thanks

 

If your bike is the 81 you say it is, you would need to check the mechanical cable that exits the top of the head and enters the bottom of the tach. If you only have wires, you either have the wrong tach or do not have an 81.
Tachs can and do stop working unannounced. Cleaning them can help but is not a regular fix. You would need to determine if yours is mechanical or electrical in order to pursue the appropriate course of action.

 

hmmm, i will have to re-look, and perhaps take pictures to post. I do have a 81 xj650. I'm not sure of the history of the bike so I don't know if the cluster has been replaced with a different year or anything though

 

If you have a mechanical tach, the cable "sprouts" out of the tach drive on the head, see: http://xjbikes.com/Forums/viewtopic/t=19538.html

The problem can be with the drive gears (rare, usually only leaks oil but they do fail on occasion,) the cable itself, or the instrument.

Mechanical Instrument 101 here: http://xjbikes.com/Forums/viewtopic/t=15303.html

Diagnosing out-and-out "not working" with a mechanical instrument would start with the cable; then the instrument, then the drive gears, in order of likelihood of failure. Of course, if you disconnect the cable from the back of the tach, and it's spinning OK when the motor's running, you've checked the cable AND the drive gears.

 

I just took the tach cable off. both ends were done up, but the cable wasn't aligned properly in the sleeve. It was too far in the tach hole, and not near reaching the other end at all. I slit it back, installed it, and it works perfectly.

thanks a tonne for the help guys. Sorry if I post questions that seem obvious. I have no knowledge at all with motorcycles, and have only driven one once for about two hours. this site is amazing in helping the "slower" guys like me

 

Old Tachs hate to be bothered showing how fast the Engine is running, this early in the season.

They need the warmth of the Sun to encourage them to respond to the impulses or the cable.

You might find that CLEANING the Tach will bring it back to responding to the rpm's.

Isopropyl Alcohol or an Evaporating Electronics Parts Cleaner.
1 -or- 2 small drops of Oil from a Precision Oiler.

Clean this Bearing / Bushing.
Hit this spot with the Oiler.
2 tiny drops.

 

He has a mechanical tach apparently, that's an electronic tach in your pic.