1981 Suzuki GS650G - dies under load when throttled past ~1/3

[seinwave]

Posting this from beside the bike. Furious and fed up.

Retimed. All is working on the ignition side (the spark looks on the weak side but it's there - edit:maybe weak enough to not work under compression? might have the timing advanced slightly too far ahead or some weak connections).

Still not a fućking peep out of the bike. Well, sometimes on the very first push of the starter it sounds like something's weakly firing. But nothing more than that.

Fuel doesn't seem to get pulled into the cylinder (the fuel line level stays about the same and I have found zero evidence of wetness on the plugs) - except when it *does* go somewhere, because the fuel line drops noticeably semi randomly. It might have happened when I undid one of the carb diaphragm covers in desperation. No clue. The bowls are full.

That would point towards a fuel delivery issue - except the bike also does nothing noticeable when I spray flammables into one of the cylinders or intakes. Do I somehow have no air getting into the cylinder??

I had to replace the tightener screw on the air filter box->rest of the airbox connector. I tightened it (and all the tightening screws - a few on the airbox->carb mouths were loose). This may or may not have caused an improvement. In any case it didn't start.

Compression is certified thumb tight.

So to summarize: I've got spark (except maybe not) but signs of no fuel, but adding fuel doesn't help, and there doesn't seem to be any air leaks, and I have compression. And no start.

Really losing patience and interest in this. I hope someone has a magic bullet suggestion and soon.

If you think I need to clean or rebuild the carbs please have a specific suggestion of what to look like. Something that would take out all four cylinders in less than three days (rode it on a Sunday, failed to start on a Tuesday). They were clean last time and I've done quite enough exploratory surgery here. If I'd bought the coils like I planned to in July I'd be on the road today.

[seinwave]

Installed (but didn't hook up - waiting on delivery of a better three-way solution than the horrible guillotine junction that comes with) the dyna today. Three points, one for posterity, one also a little for posterity (but also to check if I did things right), and one just for me.

1. I *did* have to file down the sides of the slots in the black magnetic rotor to let the advance mechanism snap closed properly. I've seen this mentioned as something you have to do with knockoff kits, but this is definitely a genuine one and I definitely had to take a fairly substantial file on each slot to allow it to close at all, and a little bit more to allow it to snap shut.

2. A little trial and error showed me that there's really only one place where the spacer/washer could go: *above* the black magnetic rotor on the shaft of the advance mechanism. See attached. There's still some play back and forth (up and down relative to this image) if I mess with the rotor/washer, so it might not quite be the right size. Do I need to add a slightly thicker mechanism or is this play alright?
20240902_151251.jpg


3. The instructions talk about timing off a fixed marking on the case, and images from other people's (non-650) bikes show a little marked disc that goes behind the signal generator. This isn't present on my bike; instead I see a little metal point (part of the case casting itself) pointing down about where I'd expect the timing mark to be. This must be the timing mark, right? I didn't snap a picture of it this time.

[seinwave]

I've kinda crossed the rubicon on the new ignition. Even if I turned back now, I think I wouldn't be confident in the bike until I did do the swap. Wish the kit was already adapted for this particular model, as I'm not looking forward to cutting the baseplate and working the oil pressure switch wire alongside the Dyna wires and grommet.

Two questions:
- The DS3-2 kit includes a big metal spacer/washer. The instructions only say that "the rotor is first installed as specified and the spacer is then put in place prior to replacing the advancer on the engine", which sounds like this goes on the shaft behind the advancer unit. Is that right?
- Do I need to have the white/black wires hooked up to the coils when I statically time the system? It'd be a lot easier if I could just plug bullet connectors from them into my test light.

[tom203]

I sold a 650 ignitor to a Florida guy who knew his failed charging smoked his original unit….I gave him a SH-232 r/r to accompany it . This was before I was schooled in the series r/r stuff

[pdqford]

Measurements on the power side look similar to last time. On the ground side, the black/yellow ground-side was dropping about 1.78V, but I found that the white (1-4) cable was dropping 11+ volts.

I pushed the white cable onto the ignition coil a little more and found that the white side cable was now dropping about 1.5V, but the black/yellow side was now dropping 11+V.

I took the white cable off the coil post and saw arcing between the spade connector and the coil post in the process. Putting back on moved the bad drop back to the white side. I tested a few more configurations and the 'bad' side moved back and forth. I didn't see any additional arcing.

Good work!
I can kinda explain what you are seeing here.
Mind you, I have never scoped an IB and can only guess exactly what goes on inside there.

When you see the ground side of the coil voltage drop jump up to 11+ volts, that indicates the IB has released the ground for that coil (you know, to make it throw a spark), and has not reconnected the ground to recharge up the coil primary again.
So now there is no current flowing through that coils circuit and therefore there is no voltage to drop.
What you are seeing is what is called open circuit voltage, aka battery voltage!

(Think of it this way: you have 12 psi of water pressure entering the hose (circuit), you loose 1.5 psi of pressure through the hose (circuit), you loose another 1.5 psi of pressure to get out of the discharge hose, and therefore you only have 9 psi available to power up the gadget (the coil primary) to do its work.

Now put your thumb over the discharge hose (unground the circuit) and stop all water flow (current). Now the pressure anyplace in that circuit will equalize and will be 12 psi (battery voltage) any place you check it.)

So when you are reading 11+ volts you are seeing battery voltage and there is no voltage drop because there is no current flow.

Folks on this form have reported that when testing for spark they get one more spark when they shut the key off. So if you are turning the key off after each measurement, I don't know exactly what is going on in that IB, but that maybe causing the IB to ground the opposite coil to charge up its primary circuit. And when you turn the key back on to measure the opposite coils voltage drop, the 11+ volts you are reading switches sides?

Note that I'm only guessing, and hopefully one of the experts on here can chime in here on what the IB strategy is.

I've always avoided leaving the key in the on position for an extended period of time as one or both coils will be sucking current from the battery and could kill a marginal battery. Not an issue for an engine that uses a crank sensor as it is smart enough to not turn the coil on if it doesn't detect crankshaft rotation.

Well, I gotta back out of here as I'm rambling again. I would suspect your coil primaries are working fine.
So I would do as the salty one above said. check out the secondary for high tension leaks.
Like in a completely dark area with the engine at idle, sprits some water on the high tension wires and see if you can cause a spark show.

[seinwave]

Well, except a $200 ignition if it blows

Jokes aside I think the charging system is in a good state right now. The quick test I did before this all got real bad was well within spec.

The reg/rec is definitely aftermarket, and I think the stator is too. That points towards a possible pathology: long-term stator issues in the custody of the PO damaged (but didn't kill) the igniter, and after the charging system got replaced the few hundred miles of riding I did (maybe more with the PO once removed) finished it off.

[Nessism]

Ignitors are often killed by high charging voltage, a result of bad R/R grounds, or an outright failed R/R. The 2nd gen 550's and 3rd gen 750's are particularly prone to this. I think you are on the right path by installing a Dyna S. Nothing to lose.

[seinwave]

Alright, took the proper tests and I think I found my smoking gun igniterwise.

Measurements on the power side look similar to last time. On the ground side, the black/yellow ground-side was dropping about 1.78V, but I found that the white (1-4) cable was dropping 11+ volts.

I pushed the white cable onto the ignition coil a little more and found that the white side cable was now dropping about 1.5V, but the black/yellow side was now dropping 11+V.

I took the white cable off the coil post and saw arcing between the spade connector and the coil post in the process. Putting back on moved the bad drop back to the white side. I tested a few more configurations and the 'bad' side moved back and forth. I didn't see any additional arcing.

There's no convenient exposed place on the ground side I could find to 'half' the circuit, but at the very least I tested resistance between where the white, black/yellow, and orange/white lines leave the coils and the molex connector where they're plugged into the igniter wires. All had negligible resistance (the black/yellow and white wire seemed to maybe show an ohm or two for a split-second a few times).

The high voltage drop and the 'switching' of where it was seems to point squarely in the direction of the igniter to me. I guess it's also possible that there's a strange sort of short inside the wrapping between the white and black/yellow wires, but that seems far-fetched and I don't have any easy way to look for a short like that without ripping most of the harness to shreds.

I'll take the next few days to prep, install, and time the Dyna-S, unless someone has another idea to where to go next?

[pdqford]

Ah, I (think I) see -- I was wrong about the O/W ignition switch wire being the 'ground' side; it is the positive/'power' side of the ignition coil. The white and black/yellow wires are the 'ground' side.

Which means that:
(meter positive) on battery positive terminal
to
(meter negative) on O/W ignition switch wire on coil
is the power side voltage drop.

And
(meter positive) on white or black/yellow wire on coil
to
(meter negative) on battery negative terminal
is the ground side voltage drop.

By golly, you got it!

The 1-4 coil dropped 1.09V (without the starter pressed) and the 2-3 coil dropped 1.13V (without the starter pressed) on the power sides.

You don't really need to press the starter button as you have shown that the battery has enough umph (technical term) to power up the starter and still have something left over for the coils.

The reason both coil's primary voltage drop is nearly identical, grab your wiring diagram, and see that each coil's power side share the EXACT same path, except for the last foot or so of the path. At that point the O/W wire splits into 2 O/W wires, with one wire powering up the 1-4 coil and one powering up the 2-3 coil.

I think that voltage drop is a little high, but at least it is what it is, and you know what it is.

Now check the ground side of the coil primary circuit for voltage drop.
The + meter probe on the white wire at the coil terminal and - meter probe on the - battery post to check the ground side drop of one coil, and then move the + meter probe to the O/B wire of the other coil to check its ground side drop.
This will check the integrity of the white wire all the way to the ignition box, the ignition box transistor and the ignition box's connection to ground and back to the battery negative post. Ditto for the O/B circuit.

Notice that on the ground side, they DON'T share the same ground path, except for the last few feet. Once they pass through their respective transistors they then share grounds with the IB ground on back to the - battery post.

So if you take the battery's voltage, minus the power side voltage drop and ground side the ground side voltage, you end up with the voltage each coil has to work with.

[seinwave]

Ah, I (think I) see -- I was wrong about the O/W ignition switch wire being the 'ground' side; it is the positive/'power' side of the ignition coil. The white and black/yellow wires are the 'ground' side.

Which means that:
(meter positive) on battery positive terminal
to
(meter negative) on O/W ignition switch wire on coil
is the power side voltage drop.

And
(meter positive) on white or black/yellow wire on coil
to
(meter negative) on battery negative terminal
is the ground side voltage drop.

(And meter positive on battery positive terminal to meter negative on white or black-yellow wire on coil (what I did above) is power side voltage drop plus the voltage drop over the coil, which doesn't mean much.)

So in conclusion the numbers I have tell us very little, except that the connections on the power side of both coils are in a similar state, and certainly don't point towards any particular wiring issue (yet).

The 1-4 coil dropped 1.09V (without the starter pressed) and the 2-3 coil dropped 1.13V (without the starter pressed) on the power sides.

I assume that the reading from battery plus to black/yellow igniter wire on the 2-3 coil is garbage data - maybe I misread the decimal point - since I really don't think there's any way for the voltage drop to lessen over the coil itself.

Thanks for your patience. I'll get proper numbers (power side & ground side, with starter pressed if I can work it) and see what comes up. This has revived hopes I just had a bad coil (the only failure mode I can think of is arcing through a badly insulated HT lead or similar, like salty_monk talks about above) and that it'll all work as desired (and keep working for more than 6 miles) when I finish my checkouts and hit the starter button in earnest.

[pdqford]

let me try this way:

The power side of the coil primary circuit runs from,
battery + post,
through a connector,
to the fuse box,
through the main fuse,
out the main fuse on the red wire,
through a connector way up to the ignition switch,
through the ignition switch contacts,
out the ignition switch on the orange wire,
through a connector waaay back to the ignition fuse,
through the ignition fuse, and,
out the O/W wire,
through a connector, waaay back up to the kill switch,
through the kill switch,
through a TWO more connectors,
and connection to the + side a coil!
(Whewh! Hope the GS650 is similar to the generic GS wiring.)

So now if you put your + meter probe on the + battery post,
and the - meter probe on where the O/W wire connects to the coil,
with the ignition switch on,
your meter will show the voltage dropped by that path (circuit) described above!
Any poor (green stuff?) connections, any crudded up switches, loose wire connectors, etc,
will impact the voltage dropped in that circuit, UP TO the coil.

How many volts is your 1/4 coil power side dropping?

Note, if in your post above, you placed the - meter probe,
on the white wire (which is the ground side of the coil primary),
then you are including the voltage dropped by the coil.

The goal is to drop minimal voltage on the power side,
and minimal voltage on the ground side, and
therefor the coil will get the maximum voltage available.

Now if your power side is dropping say over 0.4 to 0.5 volts,
grab your wiring diagram and "halve" the circuit.
With the + meter probe still on the + battery post,
move the - meter probe to maybe the ignition fuse.
If the meter reading drops, you know the worst voltage drop
is in the other half of the circuit.
So "halve" the other half of the circuit and repeat.

Not saying yours will be the same,
but on my GS750E the biggest voltage drops,
were in the ignition switch,
the glass ignition fuse,
and a factory splice hidden inside the main wiring harness.

[seinwave]

The manual is very squirrelly about which side is positive which side is negative on each ignition coil circuit. I didn't find anything when I scoured, and in any case the coils themselves are unmarked. I assume the killswitch is drain to ground, but I figured I'd just measure each possible combination.

I'll go back down and measure each pole to the negative battery as well.

Sounds like the powerside drop measurement is (+) on battery plus, (-) on igniter wire side of coil. Ground side drop should be (-) on battery negative, (+) on killswitch side of coil.

Seems like I have a bad connection somewhere on the power side of one of the coils. Likely to be the igniter, or a break in the harness?

from what I can see the only notable failure point on the power side that wouldn't affect both coils is the internals of the igniter.

[pdqford]

2-3 coil:
Battery plus to ignition switch wire (orange): 1.13V
Battery plus to black/yellow igniter wire: 1.09V

1-4 coil (where the 'bad' coil was when it went bad)
Battery plus to ignition switch wire (orange): 1.09V
Battery plus to white igniter wire: 10.91V

I understand the + meter probe is on the + battery post.
But to test the voltage drop on the coil power side, the - meter probe should be on the POSITIVE side of the coil.

To test the voltage drop on the coil ground side:
The + meter probe should be on the NEGATIVE side of the coil,
and the - meter probe should be on the - battery post.

(Effectively, the meter is providing an parallel path to the circuit being tested.
The voltage that can't get through the circuit, for what ever reason, goes through the meter, and is the voltage being dropped by that circuit.)

I'm gonna be wire color challenged as I can no longer access the GS650 wiring diagram on BikeCliffs website :-(

[salty_monk]

Try running it / starting it in the dark & look around the head. You may find the HT wires have cracks you're not seeing and are grounding out to the head. You may find moving them around (not with a bare hand otherwise it might ground the spark through you!) makes more or less sparks etc.

Sometimes people will test for spark & it looks good but the wire is not in the same location as when running it (i.e. not close enough to the head to ground out). Just an idea...

[seinwave]

No progress, but a clue.

Finally got a dry free hour to install the new coils - hadn't had a chance since I came home from my weekend trip. Resistances on primary and secondary measure good.

The battery is still strong. Right off the charger it read 13.3V, which dropped to 13.1 when I had the key and killswitch on.

Once I had the new coils installed, I tried to measure the voltage drops. I quickly realized that without four hands, clamping terminals on the voltmeter, or my fiancee to press into service, I wasn't going to be able to run the starter and get good numbers, so these numbers are without the starter button pressed (the key and killswitch were both switched to on). If these numbers are worthless or don't reveal anything, I'll get starter-on numbers as well (when the thunderstorms that chased me inside stop). But I think I *have* found something.

2-3 coil:
Battery plus to ignition switch wire (orange): 1.13V
Battery plus to black/yellow igniter wire: 1.09V

1-4 coil (where the 'bad' coil was when it went bad)
Battery plus to ignition switch wire (orange): 1.09V
Battery plus to white igniter wire: 10.91V

So it looks like there's something causing far too much voltage drop on the wire the 'bad' coil was hooked up to. I'm assuming that the absolute numbers don't tell much without the starter pressed, but surely one section of wire reading ten times the drop of the other sections is a big flashing signpost.

I noticed upon inspection that spade connector on the white wire was way looser than it should be. It felt tight in that you couldn't pull it off the stud on the coil without the expected amount of force, but even 'tightly' on the stud it rattled around easily if you shook it. I'll be cutting, stripping, and re-installing a fresh connector.

Apart from that connector:

- Is this likelier to be something bad inside the igniter, or something in the wiring harness?
- If it's in the wiring harness, any known points of failure I should look at?

(pinging pdqford as you seem to have gone through something similar with your 750)

Note: haven't started it yet; I don't want to risk killing another coil if that's what happened with this wiring issue.