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

[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.

[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.

[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

[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.

[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]

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.

[Nessism]

Could the spark timing somehow be 180 degrees out of phase? This has been a long thread, and I'm too lazy to read back through, but did you try switching coil wires from side to side? If not, it's worth a try...

[seinwave]

Hmmm, I don't think that's possible. When I timed the ignition that would have shown up in big blazing letters. The 1-4 coil (white) went high when it was supposed to (aka when I turned the advance mechanism with the advancer pointed at the full-advance mark).

I did swap wires around in the past. Might as well do it again.

My current goal is to clean up the connections to the coils and see if that does anything. Despite not seeing anything on the plugs I swear I smell gas after trying to crank it (and I really don't have a very good sense of smell). Maybe the spark really is just weak enough? The voltage drops have crawled up to 2 whole volts after I swapped the ignition (probably due to the *@%^$*@%^$*@%^$*@%^$ty hardware-store connectors I used).

[tom203]

Ok, you got fuel in bowls, spark at plugs. Activate “choke” ….make sure plungers fully extend. Use no throttle and crank….any life yet? No ? Then remove air filter element, place hand over opening to airbox to block…crank again..still nothing? remove a couple of spark plugs and look for fuel. The idea here is to ensure fuel is getting up the choke pickup tubes into carb throats.

[seinwave]

I've tried every combination of choke, throttle, and idle speed I can think of. I'll try blocking the airbox today.

I can't really find any good information on how wet a wet plug should be. Should I be looking for 'soaked' or 'slightly damp'? How long do I have before it evaporates off?

If I don't have fuel after all is said and done I'm going to be completely out of ideas. What could possibly cut off all four (or at least more than one) choke/idle tube in the carbs in the span of three days? I guess diagnosis doesn't matter much; next step will be spraying the *@%^$*@%^$*@%^$*@%^$ out of the choke pickups from below.

[rphillips]

Too much to remember back on what's been tried and done. Thinking out loud, will it start or try to start if spraying small doses of starting fluid on air filter.

[seinwave]

I tried a spritz of WD40 (I know, I know, but I had no starting fluid on hand, and also I'll take a little solvent action over starting fluid blowing a valve if I get heavy handed) in one intake (carb->engine). Nothing. I tried a spritz of WD40 in one cylinder (not the same one I tried the intake on). I *think* nothing? Maybe a tiny cough.

I haven't tried on the air filter.

If I saw any evidence of fuel getting to the cylinders I'd assume a weak spark, but I didn't. But I also don't have enough confidence that I've provided enough fuel for it to try and start, so I can't bring myself to focus on the fuel either.

I don't expect anyone to try and remember the two months of stuff I've tried. Pretty close to the point where I start going in circles, and really considering selling it to cut losses. I hate to do it to something I know *can* and *has* ran really well but this is getting moronic and I'm getting to close to literally pulling out my hair over it rather than just figuratively.

[dgates1]

Does it start with starting fluid sprayed into the carbs? Would tell you if it's a fuel delivery issue.

I recently cleaned my carbs. Found that the hole that goes to the bottom of the bowl for the choke circuit was pretty clogged, even after ultrasonic cleaning. Had to spray quite a bit of carb cleaner through each one before it finally blew a chunk out of there and they were "actually" clean and clear. Also, my number 2 cylinder would not fire the first time I started it. No fuel in that one bowl. Found a needle was sticking in the closed position just barely, like it had a little varnish still in the seat. Recleaned the seat and needle. Polished the seat with some rolled up cardboard. Put back together and had fuel to all bowls and fires on all 4. Not having that filter on the end of the needle valve seat might let a little chunk of stuff block that up.

Did you take out the fuel mixture screws and replace the O-rings there? Clean those passages all good? Did you get the old O-rings out (don't have 2 of them down there)?

I was getting the same issue where it would start fine but fall flat at 3-4k rpm, then want to die. My fuel mixture screws were about 2 to 2 1/8 turns out at the time (thought this was the factory setting on my year carbs). I reset them all to 1 1\2 turns and put the airbox in place and now will rev great all the way through. Haven't vacuum synched them yet, Morgan Carbtune tool is in the mail.

I think I read that you replaced your petcock. Make sure your new petcock is working. Make sure the vacuum line to number 2 is attached and not cracked and leaking, or hook up a temp tank. If using a temp tank, don't forget to block the vacuum port on number 2 carb.

If you adjusted your floats too far, they might not be opening up to needle.

Just sharing my thoughts and own experience... Really does sound like a fuel issue to me, but who knows now with all the ignition work you did.

[seinwave]

Well, looks like this chapter of my journey can be entered in the comedic annals of "foolish novice mechanic catastrophizes, pessimistically declares sky is falling" rather than the much sadder book of "foolish novice mechanic trusts buyer too much, optimistically buys lemon he then can't unload". The bike runs again!

Went down truly at the end of my rope to try a few things you guys suggested on this page. Decided to take the plug off the vacuum tube and reattach both hoses to the [still-original] petcock (I'd been trying to run it off just the fuel line, topping off from the tank every so often). Caused the engine to upgrade to a big cough, but only one, when I tried starting it. I think? My memory of this is sort of erased by the next thing. I might have actually done them simultaneously, and never tried to start it just after I plugged in the vac tube?

I removed the air filter and jammed a big rag into the D-shaped orifice. Hit the starter a couple times. Cough, cough, cough, and then... the glorious sound of starting combined with a "schloop" noise as the rag disappeared from sight.

Shut the engine down (it had pulled to 6k - idle was set way high). Retrieved the rag (it was just around the corner). In short order had it settled down to a nice idle and easy starts.

In my defense, the last time I had the tank on and off and tried to run it (after the first coil swap) the bike had no problem starting, running, and restarting just with fuel in the feed line and nothing in the vac line. So I hadn't even considered an open vac line could cause a problem (and I'd plugged it with a properly sized smooth stud, so I thought I'd eliminated it).

The circumstances of it starting again aren't ideal for diagnosis - not sure if it was just the vac line, if it just needed a little manual choking (the rag) to prime itself again, or if I accidentally did an "Italian carb clean" and made enough vacuum to wrench some obstruction out of the orfice it was blocking (leaving it free to settle at some unknown future date in another orfice, or an oil gallery, or or or).

I've already pulled a dubya once so I don't want to say mission accomplished yet. Haven't tried to ride it. Haven't taken it to redline (pulled smooth to 5 or 6k with about as much throttle as I expected). It started off idling way lopier than before, but after running for a while it settled down to "maybe only a little lopier than before". The left pipe spat white or gray smoke when I revved it for the first few exploratory twists of the throttle, then stopped. The right pipe oozed a little white (or gray) smoke after I killed it (not the first time it's happened). Having the air filter on or off didn't seem to do nearly as much to the idle smoothness as it should (I do think it helped a little to have it on), which means I should fast track the long-delayed Operation Weatherstrip The Airbox. But I'm really glad I'm (for the moment) back in the realm of fettling and tuning rather than lifesaving.

Thanks again to everyone for not just putting up with my longform diary posting but trying to help out, too.

[tom203]

Progress is always good! Nice work….but I still think the 115 mains are too big