1979 GS850 Ignition Trouble

[mpidsadny]

I took my freshly redone gs850 for the first ride yesterday, and it ran terrific! The power was good, idled good and sounded normal. Today, I go to take the bike out for a ride and it won’t start easily and has a rough idle. I check timing, good on 1-4, firing intermittently on 2-3. Replace both coils with some new ones that I had and no significant change. Check timing again so see so spark/flash on 2, and cylinder 3 flashes on the 1-4 mark?? Timing and firing on 1-4 is good and consistent.

When the 2-3 contact breaker is closed, the 2-3 coil gets voltage. When the 1-4 breaker is closed, both 1-4 and 2-3 coils get voltage. I’m not sure what would cause this, as I would imagine a short in the harness would also cause 1-4 to fire.

In short, after noticing intermittent firing on 2-3 I changed both coils to now observe 2-3 firing at the same time as 1-4.

I’m not sure what I changed from yesterday to today, but it appears to electrical.

[tom203]

”When the 2-3 contact breaker is closed, the 2-3 coil gets voltage. When the 1-4 breaker is closed, both 1-4 and 2-3 coils get voltage.“

sounds like a short…suspect the wiring adjacent to condensers…while your at it, replace the condensers as they can do funky things . Ignition coils on these critters are very durable, though spark plug caps can corrode and cause misfire.

[mpidsadny]

I played with the wire coming off of the point and the timing issue is resolved. The bike still runs quite poorly around idle and definitely vibrates a bit more than feels normal under load. I’m thinking it may be time to upgrade to a Dyna ignition system to not have to mess around with points, although I don’t think it will fix my issue. The wiring from points to coils tested ok as well.

[748cc]

”When the 2-3 contact breaker is closed, the 2-3 coil gets voltage. When the 1-4 breaker is closed, both 1-4 and 2-3 coils get voltage.“

sounds like a short…suspect the wiring adjacent to condensers…while your at it, replace the condensers as they can do funky things . Ignition coils on these critters are very durable, though spark plug caps can corrode and cause misfire.

I was going to suggest replacing the condensers as well. Good call on the plug caps too!

[mpidsadny]

Caps are already done and definitely improved running condition a few weeks back. I'm not sure what caused it to start running so poorly, as two weeks ago I got it running well, then parked it until Saturday to mount tires. The Saturday ride went great and yesterday it started giving issues.

Condensers are on the way as it sounds like it describes my issue. I took a deeper dive into the timing and found that the flashing of the timing light is somewhat inconsistent. It will flash consistently at a certain speed, then flash at twice the speed, creating an almost consistent beam, then maybe miss a few flashes, and occasionally it will retard timing to where the T lines up with the mark on the case, rather than the 1-4 timing mark lining up with the mark on the case. All of these conditions happening at ~1200 rpm, and idle speed is rough.

If anyone has encountered a similar issue with their points system, I'd love to hear how you all fixed it!

[mpidsadny]

Little update on the bike...

I replaced the condensers and I'm not sure how much of a difference it made, it still feels like it's running a bit rough. I disconnected the leads from the points that run up to the coils, checked for shorts and everything checked out good. 1-4 seem to be running strong and firing consistently, while 2-3 still seem to be firing intermittently, but definitely firing more than before. When I unplug a 2-3 plug cap, the bike runs poorly, but when I unplug a 1-4 plug cap, the bike dies. So far I've cleaned the points, replaced the coils, replaced the condensers, set the timing, checked the timing (before and after advance), replaced plug caps and checked for continuity/shorts from the contact breaker to the coils.

An issue that persists is when idling, sometimes the bike will sound like it completely dies, it makes a loud click, then seems to fire up again a fraction of a second after. When observing this behaviour with a timing light, it shows itself as a very short pause with no pulses, then a single pulse at retarded from where it should be (usually fire at the T mark used for setting gap) and then continues running.

If anyone has any suggestions, I'm all ears.

[tom203]

“When I unplug a 2-3 plug cap, the bike runs poorly, but when I unplug a 1-4 plug cap, the bike dies.“

the 1-4 setup is behaving normally for this type of dual plug ignition coil…the 2-3 is not, so somehow 2-3 is finding an alternative ground path. Can you go back to the 2-3 original ignition coil ( with plug wires) and see if this improves things?
the. “ loud click” gotta be electrical .

[mpidsadny]

“When I unplug a 2-3 plug cap, the bike runs poorly, but when I unplug a 1-4 plug cap, the bike dies.“

the 1-4 setup is behaving normally for this type of dual plug ignition coil…the 2-3 is not, so somehow 2-3 is finding an alternative ground path. Can you go back to the 2-3 original ignition coil ( with plug wires) and see if this improves things?
the. “ loud click” gotta be electrical .

The original 2-3 ignition coil showed the same behaviour. I can't imagine that I've had two bad ignition coils on 2-3, which leads me to believe that the issue is somewhere upstream.