Tachometer not reading accurately

1983 XJ750 Midnight Maxim.

There doesn't seem to be a turning cable coming into the tach, so I think the tach is electronic versus mechanical.

The tach is very slow to react to changes in engine speed. But when I take the bike out of the cool (45-ish) garage and ride it in 70 degree weather for a while, the tach seems more responsive, but needle movement is still very sluggish. I have no idea what revs it is doing. I just shift by sound anyways, but it would be nice if it worked properly. If its an electronic tach, the electronics would be converting the frequency of the pulses into a voltage value, and the tachometer itself is basically a wide-range volt meter. Now the needle seems to be sticky or not moving properly.

Can one disassemble, clean, re-lubircate the needle mechanism? Or just get a replacement tach off e-bay...

On an unrelated note, I was having horrible carb trouble last fall, got my carbs worked over by Ron Fowler from Edberg, he is an absolute wizard with carbs. This bike has never run better.

Thanks, Jiggs.

 

I *think* it's a cable as per the following diagram

Try to find it at the engine (it's #4 in the diagram)

 

I was under the impression that all 750s used electronic tachs. My '82 Seca 750 certainly does. Seems odd that they would go back to a cable for a later year.

My guess would be that the pivots of the tach needle have something like watch jewel oil on them, and that has dried out and gummed up. Probably it would need to be disassembled and the needle pivots and supports carefully cleaned with lighter fluid or something similar. Naphtha, maybe. Then, maybe, a very light oil, or maybe leave them dry. I haven't done this for a tach, though. I have done it for speedos. I do have watch and clock oils on hand, but most people don't, and most oils would probably be worse than no oil.

 

I had a quick look at my '82 750 Maxim and the "cable" that's referred to likely is a wire, so yeah, probably an electronic tach

would an air tool oil be light enough?

 

The cable in your diagram is a cable. It's driven by the cam. But I don't think that diagram is for an XJ750. Or maybe it's a generic XJ routing diagram so that it includes items not present in all variants.

 

It's electric. For me I had to replace my tach with a used one. You could try cleaning it but I didn't have success

 

You can pull cluster open the back of the tachometer , just do not touch needle or face plate you won't see much , use a spray nozzle with contact cleaner usually all it takes.

 

I have the same bike and tach. It is electric. I disassembled and cleaned the needle shaft. I lubricated it with graphite lubricant as used in locks. It is a dry lube. I was informed graphite lubricant is highly flammable by another member here and to be careful. I have had no issues and my tach now responds properly. Use a fast drying cleaner such as alcohol to wipe the shaft the needle rides on.

 

Correction: I was informed graphite lubricant was conductive not flammable. Use with care when applying.

 

I would assume the spay type graphite would have a flammable carrier, it does dry fairly fast.

 

Raining today, so I will take apart that tach, and clean. Be it mechanical with the centrifugal weights and springs, or the electronic type with a board and a coil and a spring, I have some contact cleaner for whatever I find.

I work with locks, and our go-to for electro-mechanical and mechanical lock-mechs is a teflon-based aerosol that works as a cleaner, and is non-conductive both before and after the evaporation of the carrier fluid. The enemy of moving-stuff is oil, it thickens and glues the parts together. Many times a lock has been "serviced" by its owner, it starts jamming, and further "owner-service" makes it worse. Spraying the lube-cleaner in the top of the lock and catching the run-off in a shop-cloth catches quite a bit of black gunk out the bottom. After about a can of ptfe dry lube in the top, the runoff out the bottom is clear, and the lock works again. We leave a couple cans of spray-lube with the owner and move-on.

I'm hoping my tach can work out as well, although my lock approach to more=better with the lube-cleaner will leave a coating of the PTFE powder everywhere. In the case of the tach, I need to stay away from the face, glass, and look-at parts, and only apply to the moving-parts.

Thanks for the chime-in. I'll post what I find.