GSX 550 ES Electronic Tachometer Question

[Guest]

Hello all, I have been lurking this forum for a while and have finally gotten around to making an account. Please let me know if I posted this in the wrong subforum.


I have got my hands on a running 1983 GS 550 E (GSX550E outside of NA iirc, quarter fairing model), as well as a 1983 GS 550 ES (GSX550ES with the half fairing) in a 'parts bike' condition (it will never run again).

Due to the poor cosmetic state of the 550E bike, I have decided to completely re-do it, with one of the biggest changes being a fairing swap to the 550ES model. Switching to the 550ES fairings requires me to install the front fairing subframe, which really bends the tachometer cable of the 550E gauge cluster in a way I would rather it not bend. To address this issue I am thinking of just swapping the gauge cluster from the parts bike too, as the 550ES cluster has an electronic tach, whose wiring allows comfortable flexibility around the subframe. I would splice the ES gauge plug into the E wires, as other than the addition of the tach wire, everything else is the same.

I ripped out the wiring harness of the 550ES to try to track down where the tach wire leads to, and while I found the male plug that it ends in, I have no clue what that plugs into as the parts bike was ripped apart and missing many things when I got it.


My question is, does anybody know where the tach wire from the wiring harness go? What does the tach wire get its reading from (I am guessing it is reading the ignition to determine an RPM)?


I am going to refer to my haynes manual when I get home, but I am not optimistic about finding an answer there, as I couldn't find one in the factory service manual, nor online.



I know that you folks love pics of bikes to go with forum posts, I will see about uploading one of the in-progress project when I get home!

Thank you and Cheers!

[posplayr]

My question is, does anybody know where the tach wire from the wiring harness go? What does the tach wire get its reading from (I am guessing it is reading the ignition to determine an RPM)?

Connect to the negative side of one of the coils.

[gsx550es]

Thanks for getting me on the right track posplayr

Update: So I checked out the Haynes manual and it turns out they have a wiring diagram specifically for my bike! All I had to do was rewire for the ES model gauge cluster which has the electronic tach and the speedometer cable output at a 90° input instead of the E model's ~60° input. Additionally I had to run a wire from the male connector's tach wire to the circuit which connects the 3rd spark plug coil to the igniter unit.

While the electronic tachometer now works, while revving the engine at neutral now, the tachometer has 'flat spots' as I steadily increase the rpms. Any idea why this might be happening?

[gsx550es]

Bump on this post for any answers

To clarify, the flat spots are only on the tach, when I progressively throttle the engine (in neutral) the engine RPM audibly rises and falls smoothly, only the actual tach seems to hang up at spots during throttling up. Moving the needle with my finger, I don't feel any particular spots of resistance.

[posplayr]

While the electronic tachometer now works, while revving the engine at neutral now, the tachometer has 'flat spots' as I steadily increase the rpms. Any idea why this might be happening?

I doubt it is electronics, but rather friction in the mechanism.

http://electricalengineeringdesigns.blogspot.com/2012/06/darsonval-movement-how-ammeters-work.html

The needle is probably being held down by gravity and a small EMF force is pushing the needle up. It would not take much friction.

[GregT]

See if it moves freely with the gauge face horizontal.

[greg78gs750]

while i would defer to posplayer on electronics expertise, it is possible the tach is going bad, very common on the e-tachs from this era. possible? I replaced the gauge cluster with a gsxr clockset on my 1100es to get a functioning tach

[posplayr]

while i would defer to posplayer on electronics expertise, it is possible the tach is going bad, very common on the e-tachs from this era. possible? I replaced the gauge cluster with a gsxr clockset on my 1100es to get a functioning tach

IIRC most of the bad electronic tachs are due to degradation of the electrolytic capacitors (very common for all electronics especially power supplies). Those tachs seems to exhibit bouncing needles rather than "flat spots' which I interpret to mean changes in sensitivity to RPM change. This is the reason i assumed a mechanical problem.

[greg78gs750]

yeah, i'm out of my depth here i know. I hear "e-tach" and i know one thing lolz

[gsx550es]

Bump on this old thread.

I have mothballed the project for a while but picked it back up and finished it this past weekend, though I am still working on ironing out some kinks.

I got the thing on the road and I immediately noticed that the tach isn't too accurate or reliable.
As I mentioned before in this post, I rebuilt a 550E to an ES fairing style, which included swapping a gauge cluster from an ES for the electronic tach on the ES because the mechanical tach on the E interferes with the fairings subframe with its tach cable.
The tach displays 0-3500 fairly well, pretty smoothly, and without much residual needle bouncing. The tach experiences trouble after 3500 however, where sometimes the needle hovers around 4-5k despite me obviously increasing the revolutions well past that and eventually suddenly shoots to 10k, or sometimes the needle jumps wildly in the higher rpm range, not showing me an accurate reading.

I am interested in any advice on troubleshooting this, or any guide on testing the tach to see if the tach is problemed as I cannot seem to find any real guides on that online

edit: to add, moving the needle with my finger doesn't show any friction resistant at any point in the needle's rotation.
I would like to keep the original style gauge cluster to suit the bike aesthetic and all, so I intend on avoiding swapping the cluster altogether, though worst case scenario if the tach is not salvageable, I think I would look into putting a new aftermarket tach behind the cluster face plate to get a functioning tach but maintain the original look, though I want to positively make sure that doing that is absolutely necessary.