1981 GS650 Ignition issues - No Spark to Cylinder 1 and 4

[Guest]

Hi everyone,

I'm still fighting with this 1981 GS650G. Fuel/carb work is complete but now for some odd reason I'm not getting spark to Cylinders 1 and 4; 2 and 3 are fine. I've swapped plugs around to confirm its not them. Coils have voltage. It's just odd that each coil is only sending a signal to one of the two cylinders its assigned to. I'm not sure how the signal generator works and whether or not that may be my issue. Any help is greatly appreciated.

Thanks,
Tony

[tom203]

The signal generator fires 1 and 4 together ,then 2 and 3 together- this is a "wasted spark" system. Make sure all connections from signal coils to ignitor and from ignitor to ignition coils are good. The signal generator works by that little tab on revolving rotor spinning by a signal coil - this tells the ignitor to fire that ignition coil that corresponds to that signal coil (either 1 and 4 or 2 and 3). Connections are critical since it's a small pulse.

[awilchiwsky]

Thanks for the help. A little odd that two cylinders would fire at the same time when needed...but if it works.

Anyways, all wires look like they're attached. Before I check for continuity, is there a way to test the signal generator itself to make sure it's even sending a signal?

[tom203]

Thanks for the help. A little odd that two cylinders would fire at the same time when needed...but if it works.

Anyways, all wires look like they're attached. Before I check for continuity, is there a way to test the signal generator itself to make sure it's even sending a signal?

Go to this link step 14- or or just start from step

http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17

[awilchiwsky]

It's been a while. Sorry. I tried testing with the AA batteries and didn't get anything. Not sure where to go from here. Any help is appreciated to get this bike back on the street.

[tom203]

Take fuel tank off, so you can see ignition coil connections -clean them . The ignition coils are connected to ignitor by a 4 wire plug (under seat )make sure this has good contact. Since you say you got spark on 2and 3, switch the connections that are on 2 and3 ignition coil with those on 1 and 4. Remove spark plug from #4, reconnect its plug wire- holding plug against engine, press starter button and observe spark. If it now sparks, then either your 1 and 4 ignitor-to-coil connections are faulty or your ignitor is bad.
if still no spark, then bad coil, plug wire or plug caps on that coil. Remember that with this twin spark system, the spark has to travel down one plug wire, leap gap then "find" other plug, leap that gap to complete circuit.

Edit: put bike model/year in your signature

[awilchiwsky]

So if I switch the coil wires I can get the other plugs to fire. So it seems like the LH coil doesn't work but the resistance tested ok. How do I check the signal generator again? Is there a way to install it incorrectly? I thought it worked when it was on the old motor..but I'm not 100% sure about that. The bike sat for 10 years. New motor has great compression and carbs are rebuilt. Just not gettin spark every where.

1981 gs650g

[awilchiwsky]

resistance across the signal generator (blue and green wires) is 307 ohms. on here it says we're good if its between 250-350 ohms. so I couldn't switch the 4 wire plug around to try and get the opposite coils to fire. I had to do it at the coil end of the harness. I tried using the 1.5V battery to test the igniter and got no where. none of the spark plugs would fire during the test, but in reality 2 and 3 are ok. is there a more reliable test? if not, another way to test the coils? at this point I believe its either a coil or igniter issue. thanks for the help.

-tony
81 gs650g

[tom203]

To clarify.....At the connections on ignition coils...... Each coil has an orange/white wire and either a solid white or yellow/black wire- the latter are from the ignitor via that 4 way connector. Swap the y/b and white wires ( i.e.,to opposite coil). Crank it over and observe spark at #4 or #1
Your signal coils test fine. These were from donor bike? Do you have spare ignitor?

edit: make sure signal coil for 1 and 4 has not loosened up on mounting plate causing excessive clearance between coil face and revolving tab

[awilchiwsky]

Thanks for your help so far Tom. I Swapped wires at coils to see the spark at 1 and 4 but not at 2 and 3. I tried to use clips to switch at the 4 wire plug but then couldn't get any spark anywhere. What should be the gap at the revolving tab?

[tom203]

Thanks for your help so far Tom. I Swapped wires at coils to see the spark at 1 and 4 but not at 2 and 3. I tried to use clips to switch at the 4 wire plug but then couldn't get any spark anywhere. What should be the gap at the revolving tab?

Leave the 4 way plug as is- just interchange the white and y/b wires at coils and see if 1 and 4 fire. This tests the ignition coil secondary circuit on that coil using the part of ignitor that you know works for 2 and 3.
the gap to tab should be similar on both signal coils.maybe 1/8 inch??

[awilchiwsky]

If I switch the cables like you say I get 1 and 4 to fire.

[awilchiwsky]

I checked voltage at the blue and then green wires coming from the signal generator. Both are the same, approx .3-.4V. This should be telling me the generator is ok. Now I'm down to either igniter or coil being the issue.

[tom203]

"If I switch the cables like you say I get 1 and 4 to fire."
this means that the coil is ok , so it's either in ignitor, or the wires from ignitor up thru the connector and on to the ignition coil. Probably the ignitor, but check the wires.

[awilchiwsky]

Is the igniter under the air box?