Tacho shoing x2 RPM

When all the smoke has escaped from inside the wires...
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Adam
Posts: 32
Joined: 01 Aug 2020, 16:51

Tacho shoing x2 RPM

Post by Adam »

Hi,
I just bought a 'new' Zephyr 750 C2 last week and am very much enjoying it, not haven ridden a big bike for 12+ years.
Until yesterday, the tacho showed the correct revs, but has switched to showing something close to double.
Doing 40 in 3rd was showing about 5000 RPM - but I looked down and saw 10,000rpm!
If I go faster, the rev counter needle points straight down.

The battery seems fine - no problems starting and measures about 12.7v. I've been out a few times with it like this, always with the headlights on, and I just put it on charge and it shows 75% charged, so it appears to be charging OK - no alternator or voltage regulator issues

I've fitted an after- market alarm, but that was days ago and I've used it since then and the tacho was correct, so I don't believe that it the issue.

Any ideas?

Thanks!
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: Tacho shoing x2 RPM

Post by Freddy »

Adam wrote:Hi,
I've fitted an after- market alarm, but that was days ago and I've used it since then and the tacho was correct, so I don't believe that it the issue.

Any ideas?

Thanks!
Still that's were I'd start. Disconnect it for a while to be absolutely sure it isn't the problem.
Adam
Posts: 32
Joined: 01 Aug 2020, 16:51

Re: Tacho shoing x2 RPM

Post by Adam »

Thanks - I shall give it a go!
Adam
Posts: 32
Joined: 01 Aug 2020, 16:51

Re: Tacho shoing x2 RPM

Post by Adam »

Unplugged the alarm - and no difference. Still showing x2 RPM

Any other ideas?
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: Tacho shoing x2 RPM

Post by Freddy »

You didn't by any chance disconnect the ignition coil 12V connections when you were fitting the alarm, or have broken into a black wire???

The reason I say this is looking at the wiring diagram for the tacho in the service manual there seems to be 3 wires running to the tacho. A brown that just seems to be power when the ignition is turned on, a black/yellow being an earth, and the only one that looks likely to control anything is a black wire that comes from the connection between the ignition coil and igniter (ICU).

The black coil wire came from the factory attached to the inside connector of the left side coil, red wire on the outside connector. On the right hand side its a green wire on the inside connector, red again on the outside connector.

I've always made sure the 12v coil wires are connected to the coils the same way they were originally. I have no idea what happens if they are put on the other way around, never having done it. But purely grasping at straws, I'd check the 12v connectors are on the coils the way I describe.

You can easily see the coil connector wires without removing the petrol tank. They are just up under the tank basically in line with carburetor intake manifold.
Adam
Posts: 32
Joined: 01 Aug 2020, 16:51

Re: Tacho shoing x2 RPM

Post by Adam »

I didn't change anything else when fitting the alarm, but I will have a look at the coil wiring and see if anything doesn't look right
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: Tacho shoing x2 RPM

Post by Freddy »

Adam wrote:I didn't change anything else when fitting the alarm, but I will have a look at the coil wiring and see if anything doesn't look right
Out of ideas. You can try the test procedure outlined in the workshop manual, but somehow how I don'y know it will help as the tacho hasn't stopped working all together. What it involves is .......

Remove the fuel tank
Remove the Black lead on the ignition coil
Turn the ignition switch ON
Connect the black lead to te positive battery terminal using an auxiliary lead. The tacho needle should flick
Turn ignition switch off
** If the needle does not flick, replace the tachometer unit.

Before doing that test I'd make sure I have a complete circuit from the coil black wire connection to the tacho using the resistance function of a multimeter. A $10 Chinese made one from a big barn hardware store is good enough for basic motorcycle work. Usually yellow with a dial in the middle. Basic so easy to understand.
Adam
Posts: 32
Joined: 01 Aug 2020, 16:51

Re: Tacho shoing x2 RPM

Post by Adam »

Will, I finally found the problem!

I'd removed the tank just to have a look underneath, and to see if there were any loose connections that could explain the tacho behaviour. Everything looked good.

I put the tank back on and started the bike - it ran for a few seconds, and then stopped.

On trying to start it again, the engine turned over but showed no sign of wanting to start.

I removed the tank again, and checked all the connectors to the coils (I'd removed a wire to check the tacho - that was fine) and make sure it's missed nothing.
Also checked the fuel pipes - there's a lot of peeling tank liner in the tank - that's another story) but the inline filter was clear and full of fuel, so that didn't appear to be the problem.

So back on with the tank. Still no joy from the engine though, so what else could be wrong?

The engine sounded like there was no spark, but I wanted to be sure.
I removed sparkplug no. 4 and with a rag over the hole and the plug touching the bolts on the exhaust I turned the engine over - no spark.

So, off with the tank - again - for a further search for the 'lost spark'.
A 12v tester confirmed the red wires to the coils - and the black and green wires going to the ingnition unit had 12v, so there was power to them and the coils weren't open circuit.

I removed the battery and pulled out the IC Ignitor ignition unit and checked the connectors - that was all good. I was running out of ideas! :?

Looking in the Kawasaki workshop manual (thank you Drayton Croft motorcycles in Hinkely for selling me one of those - even though it is second hand and a little dirty, it is better than the Haynes manual) it showed the connector for the wire that runs from pickup coil to the IC Ignitor.
This sits on the right-hand side, next to the battery.
I disconnected it and put it back together and then I noticed something.
Pickup coil connector
Pickup coil connector
The black/white wire - the center one - the little metal connector you can see through the plastic, was a little higher than the other two.
The top part of the connector has the male connectors and it had come a little loose from its place and moved up - so it wasn't connecting to the female connector in the lower part.
I pulled the connector apart again, pushed it down and made sure it stayed in place when I put it together again.
Even without the tank on, I turned the engine over and it spluttered into life :D

So, tank back on, it started and ran- so off out for a ride and guess what - the tacho was showing the correct reading again! 8-)

I think this connection must have been just connecting, just enough to make the bike run, but poorly enough to upset the tacho.
ZoneAdmin
Site Admin
Posts: 130
Joined: 09 Aug 2017, 13:52
Location: Cwmbran, Wales

Re: Tacho shoing x2 RPM

Post by ZoneAdmin »

Good investigation work Adam.

Regards
Dennis
Regards
Dennis

Current bikes: Zephyr 750 C4, Zephyr 750 C3
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Previous bikes: Kawasaki Z1000 A2, Kawasaki KH400 A4, Kawasaki KH250 B1
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Ivor
Posts: 239
Joined: 06 Sep 2017, 20:49
Location: Hampshire UK overlooking the Needles :)

Re: Tacho shoing x2 RPM

Post by Ivor »

Well done on sorting it and thanks for telling us what you found. That's what keeps the forum alive and helps others who might have the same/similar problems :D
1995 ZR1100A2
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