ZXR750 L1 Tachometer/Electrical Problems

Hi all,

I'm trying to troubleshoot a couple of niggling issues I've got with the bike, basically I have a tacho which is not registering revs, once in a while it skips up to what I would assume is the correct rpm but dies back down to zero within a short amount of time(few seconds give or take). So far I have connected 2 different tachos to check, both are having the same problem. (Both tachos could be shot, but that seems unlikely)

Note: Bike is running very well, I have no issues with the running condition.

so far I have done:

- Cleaned and roughed up battery terminals and connectors
- Checked continuity of all wires within tacho signal and power circuit (Black wire on the loom, taking signal from 1&4coil) - All are good
- Checked pickup coil resistance (I would assume that this is creating the signal? Is that right?) I found the resistance between the top bolt of the pickup coil(the one where the wires exit from) and ground to be 0ohms, I'm not sure if I tested this right but if 0 ohms is the correct measurement then my pickup coil is faulty. If my pickup coil is faulty shouldn't the bike be running differently?
- Checked engine ground, which has a little rubber boot on it, it is completely rust free.

Still, no matter what I do, it won't work. I'm totally out of ideas. Does anyone have any experience with this or know of any common problems? Any advice?

Thanks a lot for your help, electrical issues are very frustrating.

Aj

Hi AJ,

Great to meet you on Saturday, and sorry the tacho didn’t fix the problem. As you say, I can’t imagine you’ve got two dodgy tachos, so it’s obviously something else. The way its acting, it almost sounds as though its acting like a relay – something heating up, and a circuit breaking when it gets to a certain temperature. I don’t believe there’s any kind of relay in the tacho circuit, though.

I’m not convinced on the continuity side, and I reckon a good test would be to create another set of wires from the tacho to the respective source, and attach it to the loom. If it works then, you could test each wire individually to find the break.

Cheers,
Brian

PS On reflection, I think that small relay was for the fuel pump. I’ve found another relay if its of use, a round pot that looks like its from the indicator circuit – let me know if you’d like it and I can throw it in the post (or feel free to drop by again sometime).

Hi Brian,

Definitely great to meet you as well! No worries, I now have a spare if I need it. I think you could be right about the relay, the signal wire which has the square waves coming from the pickup coil is going through the ignitor unit, so replacing that might yield some sort of result. Unfortunately, I don't really have the option to go hunting for one, and the bike is still running perfectly.

I agree, my continuity test is not telling the full story. I think to set up a separate circuit would work, so far, all I've done is set up a jumper for each individual terminal on the tacho, but I didn't jump all three at the same time. With one jumper on each lead I still didn't get anything from the tacho. Now that I think about it, these tachos would be analog so they would have a little 9v battery inside to count time between pulses of the square wave, so it could be that that little battery is completely dead now, which would mean I have to rebuild the tach.

Yeah, thanks for that relay, I really appreciate it. Always good to have spares when it's about the age when all these bits start perishing. I won't need the other relay as I've got a few spares of those now, but I appreciate the offer and I will definitely drop by on my next ride up the old road!

Cheers,

Aj

Sorry for the (typical for me ...) super-slow response, hope the problem has sorted itself.

Cheers,
Brian