No spark!! Need help.

[Guest]

Hey guys I?m new to this forum. Hope to get some help with my 1980 gs750e that I got off someone online that was in garbage condition, wiring harness was basically all gone and it wasn?t running. I first figured I would start by getting the wiring harness done and then see what was the issue with the no start issue. These are the things I?ve done so far.

I installed an M unit since buying a OEM harness was so expensive and used ones weren?t cheap either. I wired lights, tach, tail-lights. Now it was time to diagnose the no start issue. It cranks, but doesn?t have spark.

Checked Battery
solenoid
R/R
Stator
Spark plugs (tested at 4ohms)
ignition Coils (tested at around 4.1ohms)

This bike has An electrical ignition which I?m not familiar with and might be missing parts? I?m pretty new to motorcycles so if I?m missing anything on the ignition side please let me know.

I?m assuming it could be my clutch safety switch, its wired to ground and the yellow cable running off the solenoid. Then the kickstand switch I don?t see any sensors in the kickstand, there?s also the neutral safety switch which is connected (dark blue wire) to my tach.

what could be my issue? What should I be check now? Could it be the wiring on my M unit? If I?m using the M unit with momentary switch should anything be on the kill input of the m unit? Please help!!

 

[Rich82GS750TZ]

Oh boy, where to start!?

Get the factory service manual from BikeCliffs Website. Link in Signature. You want the GS 750 16 valve one in the top section, middle column. There?s also a very good color wiring diagram in the right column. You need that.

Create a signature with your bike year and model(at least). It?s under Settings at the top right of any Page.

Sorry, I?m no help with the M Unit.

You can learn how to post better and more pictures to the forum in the Imgur thread linked in my signature.

Welcome to the GSR. You?re in a best place to help you get this bike on the road.

 

[Guest]

Oh boy, where to start!?

Get the factory service manual from BikeCliffs Website. Link in Signature. You want the GS 750 16 valve one in the top section, middle column. There?s also a very good color wiring diagram in the right column. You need that.

Create a signature with your bike year and model(at least). It?s under Settings at the top right of any Page.

Sorry, I?m no help with the M Unit.

You can learn how to post better and more pictures to the forum in the Imgur thread linked in my signature.
Welcome to the GSR. You?re in a best place to help you get this bike on the road.

thanks! And yes I got the owners manual and have been on bikes cliffs site for most of my research. I?m completely new to motorcycles, but trying to learn to repair everything on my own to learn. I?m just stuck because going back and fourth from colored wiring harness to the diagram of the M unit is confusing. I hope it?s just the safety switches, but I dont have the kickstand sensor, and clutch is connected to the solenoid, and then N light switch is already connected to my tach. Hopefully someone can suggest something. I?m going crazy haha

 

[Rich82GS750TZ]

Seems right that clutch is connected to solenoid. As for the kickstand sensor - It’s just to illuminate a light. It does not have a start defeat function.

 

[Redman]

In stock config:
- the clutch switch is wired in between between the starter button and the starter solenoid. So that have to hold clutch lever it to operate the starter solenoid/motor. That is all, not any interlock to the ignition.
- the sidestand switch (if is one) completes the ground to light the sidestand light on the dash . That all, lights a light, not interlock anything. And a confusing situation in that the oil sensor lights both the oul
light and the sidestand light.
- the neutral switch completes the ground to light the neutral light. That is all, no interlock of anything.

so, none of that should interupt the ignition spark.

what you have not
mentioned is if you have a good 12 volts to the coils (what was the org/wht circuit).

?. And 12 volts to the ignitor.

 

[Guest]

Not sure what you mean? Do you mean the ohm reading of the coils? Or voltage going from battery to the coils? Cause I?m not sure how you do that. Do I check that by using the positive probe on the positive side of the coil and the ground side to ground while ignition is turn on? Sorry I?m a noob still. But thanks for the heads up on the switches!

 

[Redman]

??
??..Do I check that by using the positive probe on the positive side of the coil and the NEGAtIVE PROBE to ground while ignition is turn on? Sorry I?m a noob still. . . .

Yes. Both coils .

 

[pdqford]

I’m trying to follow along on this thread.

I’m kinda new to some of this terminology.
What is and who makes this “M unit” you installed and what is it supposed to do?

I apologize for my lack of understanding.)

 

[Guest]

Yes. Both coils .

so I tested and there?s no voltage to the coils, I cranked it and nothing. Batteries at 13v.

 

[Redman]

so I tested and there?s no voltage to the coils, I cranked it and nothing. Batteries at 13v.

Well, THAT is a problem.

In original wiring, and he ignition fuse powers the kill switch, thru kill switch goes to starter button and to coils and to ignitor.
I don?t know what you did with this ?M unit?, (actually I don?t really know what a M unit is) but I think you need power to the coils, and the ignitor unit responds to the ignition pick up, and the ignitor unit then operates the coils.

 

[Redman]

For general info, for me and others about M unit

https://technicalarticles.revivalcy...31-m-Unit-Blue-Basic-Universal-Wiring-Diagram

https://motogadget.com/shop/media/downloads/manual/munit_blue_manual_1.8_en.pdf

 

[Guest]

Sorry I thought you were being sarcastic about the m unit. But it?s basically a fuse box computer? I guess that?s how I would describe it. It eliminates majority of your wiring harness. I only got it because the bike I got had a horrible wiring harness missing a bunch of thing and it was a fire hazard. Plus I wanted to add tach and stuff, but basically that?s what it is, there?s a wiring diagram for it that I think I might have wrong.

for your comment about the power ignition coils and you said the pick up coils, does it matter if I have an electronic ignition? Is there even pick up coils if I have the electronic ignition? Sorry not much info on pick up. Im thinking this might be a CDI issue? My stator is new, R/R js new, my battery was built by me with lifepo4 batteries and a 200a bms which should be more then enough to start the bike.

 

[Rijko]

I have the M-unit, the black version 2.
Have collected lots of info like wiring schemes etc here

I take it you have the new version 3, M-unit Blue ?
There's control lights on the M-unit that light up.
That's a good place to start : it tells you if the M-unit switches on the 12 volt ignition output.
M-unit switches off the power output when it detects an issue (and restores it when the issue is solved),
and will blink the output led to indicate an issue.

If your bike is wired correctly there should be a 12 volt output from M-unit to ignition/igniter and coils.

 

[pdqford]

Thank you Redman for the website describing the “M Unit”.

So, Bulldozaaa, please describe how you have your ignition coils circuit wired with this M Unit and how you have the ignitor circuit wired.

 

[allojohn]

Is the kill switch on RUN?

 

[Guest]

I just disconnected the kill button I have since I think the momentary switch is suppose to be the start and also kill, I don?t think it needs a separate button. I believe I have it correct. My electronic ignition is reading 30ohm of resistance so I?m guessing that can be an issue? It?s suppose to be 20ohms max according to owners manual. And after that all I have left is CDI. I just compression test and all four cylinder was at 110 (cold) so higher if it was tested warm. I tested everything else already, with good parts on a different bike.

 

[Guest]

In stock configuration:
- power from battery goes through main fuse to ignition switch, back to fusebox, through ignition fuse, then to kill switch.
- from the kill switch power then goes to the starter button and the coils/ignitor.
- power from the starter button goes through the clutch 'safety' switch to the starter solenoid (many of us have bypassed the clutch switch)
- power from the kill switch goes through the coils, then the ignitor to ground. The ignitor is just a box of transistors that replaces mechanical points. Nothing exotic, not "CDI", just a box of transistors.

I have seen several mentions of M-units, but most of them were installed by choice, not by necessity, to replace a harness. Part of your problem is that there are far too many unknowns. Eliminate them one by one, you'll get there.

 

[pdqford]

I just disconnected the kill button I have since I think the momentary switch is suppose to be the start and also kill, I don’t think it needs a separate button. I believe I have it correct..

Without you describing how you have it wired, I have no idea if it’s correct or not. But if you believe you have it correct, that’s what matters.............

 

[Guest]

That was very good info! Thanks man. Ima trace it like you said, probably look up how to bypass the clutch safety switch in the meantime while I?m waiting for the pickup to deliver. I had no choice to switch to m unit or buy a new harness which is pricy as well. I wanted to add other stuff as well like tach and a few other things and I figured the m unit would let me get rid of the bundle of wiring. But thanks for the tips, I?ll test out those things and report back.

 

[Guest]

Sorry, let me try the testing sequence for the no spark, I would tell you how it?s wired to the m unit, but I haven?t had time to sit there and write it out, but I will if I still can?t figure it out. I already know that I don?t have the starter button wired to the clutch safety switch that runs into the solenoid. So I will check that tomorrow and if that?s not the solution then I?ll do my wiring diagram. Thanks