Thank you all for the input,
As I havew said it's 99% an electric issue, as the engine, carbs, fuel lines, petcock are swapped from a crashed bike that was working.Also ignition box, coils (the ones bolted on the frame under the tank) with spark-plug cables are swapped as well. It must be a corroded connection somewhere, but i haven't been able to trace it till now... let's see...

Any ideas where to look at from people facing similar (electric) issues, are most welcome

Next time you go to start it, put it on the centerstand with a fan blowing on the motor. Let it run for 20-30 minutes and see if it shuts down again. If yes, something is overheating. If no, you have a wire vibrating loose. My money would be something is overheating though.

Thanks Big Rich, the thing is that it won't start again! Every time it dies, it won't fire up from then again, until i unbolt the whole crap and do sth with no meaning at all. Then it will start just to give me hopes, make me drive it again for a small ride, give me more hopes that it's ok, make me drive it again for a long ride, where it will die leaving me out in the dark with a f$%ing pile of shaZam! that won't move it's stinking butt...

Quote from: gsdox on June 20, 2011, 02:56:13 AM
Thanks Big Rich, the thing is that it won't start again! Every time it dies, it won't fire up from then again, until i unbolt the whole crap and do sth with no meaning at all. Then it will start just to give me hopes, make me drive it again for a small ride, give me more hopes that it's ok, make me drive it again for a long ride, where it will die leaving me out in the dark with a f$%ing pile of shaZam! that won't move it's stinking butt...

Sounds like the primary ignition circuit ... iirc you said you put a different (used?) igniter on the bike - how do you know that igniter is good ?  or that if it was good initially, you may have damaged it somehow (like maybe your voltage/regulator allows too much voltage or ac into the circuit).

I've seen several igniters fail in different ways - bike starts fine, runs strong for 5 minutes, then sputters and shuts down. Or there is a lack of power, one cylinder dropping out intermittently, etc)

To operate properly that igniter needs constant '12vdc'  from the battery thru the orange/white wire thru the four pin igniter connector . That means all the switches and connectors on that circuit must be good for the thing to run.

Or, that same circuit powers the ignition coils so likewise must be good, and then from the ignition coils two wires must be continuous to the igniter - white, and black/white (?) - for those to operate.

The ground wire from the igniter must be unbbroken to battery ground.

All in all not complicated, but seems like it if you haven't isolated the problem.

Me, I would just bypass the whole mess with a temporary circuit of correct gauge wire and a on off switch - Dangerous as hell to ride the bike like that 'cuz your bypassing the safety switches ... but that's sometimes what you gotta do to get an old vehicle running enough to figure it out.  Or eliminate electrical as cause of the problem.

Sounds like you need someone more experienced to help you out.

Bigfatcat you're so right that i need someone more experienced than me to help me sort thing out. Finally i might have to get the bike to an electrician, but that, apart from the money it will cost, is a hard task, as I will have to have the bike towed or sth. It should be what you suggest, my bike behaves like you have described, but i'm now totally devastated to think that i might have destroyed two! ignition boxes and that I might also need a regulator... but that is the sad true, i guess.

Anyway could you tell me a bit more about the temporary circuit? Is going to connect the positive of the battery straight to the ignition coils or what. Please excuse my luck of knowledge and silly questions... And thank you so much for your advice, things seem more certain now in my head...

Quote from: gsdox on June 20, 2011, 11:54:35 PM
Bigfatcat you're so right that i need someone more experienced than me to help me sort thing out. Finally i might have to get the bike to an electrician, but that, apart from the money it will cost, is a hard task, as I will have to have the bike towed or sth. It should be what you suggest, my bike behaves like you have described, but i'm now totally devastated to think that i might have destroyed two! ignition boxes and that I might also need a regulator... but that is the sad true, i guess.

Anyway could you tell me a bit more about the temporary circuit? Is going to connect the positive of the battery straight to the ignition coils or what. Please excuse my luck of knowledge and silly questions... And thank you so much for your advice, things seem more certain now in my head...

I'll make a video use my gs and post it, maybe today if I can scrounge some time .

I doubt you destroyed your igniters, just one of several possibilities, so don't worry about that yet.

Quote from: gsdox on June 20, 2011, 11:54:35 PM


Anyway could you tell me a bit more about the temporary circuit? Is going to connect the positive of the battery straight to the ignition coils or what. Please excuse my luck of knowledge and silly questions... And thank you so much for your advice, things seem more certain now in my head...

I made a video describing what i'd do in your situation - let me know if u want it .

sorry guys (and especially to you bigfatcat) for not dropping in, I have moved and don't have internet at my new place for the time being...

Of course i want the videobigfatcat, thank you a lot ! Please tell me what i have to do to get it!

PM to u, gsdox.

Still waiting to see the metal eating display

Michael

So many issues at once are difficult to diagnose.  A new motor was in order but this bike like any other modern bike I know of won't run worth a damn without a good battery.  All street bikes I know of made since the early 70's have battery ignition, meaning the ignition runs off the battery and the alternator/rectifier/voltage regulator charges the battery, meaning the bike won't run for crap without a good battery.  My first dirt bike was made that way and Jack Benny was still alive.  If you don't know who Jack Benny is don't tell me, I don't want to know!  You can't just jump it and ride it.  It's not a car.  A bad battery will cause weak ignition, especially at higher rpm, and can overload your charging system, even to the point of causing voltage regulator failure.

As for the idle hanging, you probably still have dirt and/or wear in your carb slides, making them stay up longer than they should, assuming your diaphragms are in good shape and the vacuum tubes are connected and not cracked.  My idle was hanging quite a bit when I bought this thing once it got good and hot.  I just kept putting Marvel Mystery Oil in the gas and kept riding it and it mostly went away over time.  It will still hang at about 2,000 rpm after riding for an hour at highway speeds, but after 15 seconds or so it will settle to a normal idle.  If my trips are under an hour, which is almost always, it doesn't happen.  Some guys get all bent out of shape over hanging idle and it's no big deal to me.  To me it's not a rideability issue.  Don't give up, you're almost there!

Quote from: bill14224 on July 02, 2011, 02:01:06 PM
So many issues at once are difficult to diagnose.  ...[ much wisdom ]...  A bad battery will cause weak ignition, especially at higher rpm, and can overload your charging system, even to the point of causing voltage regulator failure...

[ more wisdom ].

Jack Benny ? Then u may have heard the old saying among mechanics "Most carb problems are electrical", meaning that electrical issues can be mis-interpreted  as carburetor faults.  Especially true back in the days of 6 Vdc systems.

Good battery very important - I was guilty in the past of running cheapo autozone/wal mart crap batteries and even new they would sometimes give problems, often not holding a charge if the bike sat for a week or so ...

And that's a really good point about the gs500 ignition system being 'battery powered' - the ignition coils are battery powered, as well as the ICU.  I've seen the mistaken notion on this board  that the gs500 has a 'cdi' - no it's not. That's for higher compression, higher revving engines.

Hopefully gsDox can troubleshoot his ignition and find some simple fault easily corrected.

Better than eating an iron salad.

Thanks a lot to you all and a special thank to bigfatcar who got himself in a lot of trouble just to help me. I'll keep you posted about my efforts, but it's going to take a while, as i have moved but haven't got everything to my new place (the gs is still waiting).

Quote from: bill14224 on July 02, 2011, 02:01:06 PM
So many issues at once are difficult to diagnose.  A new motor was in order but this bike like any other modern bike I know of won't run worth a damn without a good battery.  All street bikes I know of made since the early 70's have battery ignition, meaning the ignition runs off the battery and the alternator/rectifier/voltage regulator charges the battery, meaning the bike won't run for crap without a good battery.  My first dirt bike was made that way and Jack Benny was still alive.  If you don't know who Jack Benny is don't tell me, I don't want to know!  You can't just jump it and ride it.  It's not a car.  A bad battery will cause weak ignition, especially at higher rpm, and can overload your charging system, even to the point of causing voltage regulator failure.

As for the idle hanging, you probably still have dirt and/or wear in your carb slides, making them stay up longer than they should, assuming your diaphragms are in good shape and the vacuum tubes are connected and not cracked.  My idle was hanging quite a bit when I bought this thing once it got good and hot.  I just kept putting Marvel Mystery Oil in the gas and kept riding it and it mostly went away over time.  It will still hang at about 2,000 rpm after riding for an hour at highway speeds, but after 15 seconds or so it will settle to a normal idle.  If my trips are under an hour, which is almost always, it doesn't happen.  Some guys get all bent out of shape over hanging idle and it's no big deal to me.  To me it's not a rideability issue.  Don't give up, you're almost there!

small hanging idle isnt a problem... but a high one 3K+ is dangerous... I know first hand as my bike tried to kill me because of it... It was a lot of inexperience and right shaZam! at the wrong time but I fell because I accidentally forgot to cover the clutch in a parade, the idle hung, I tried to stop going down a hill and somehow did a stopie, the bike reved up and spun the tire and when the back hit again it was bad news... perfect storm but possible with a 3k+ hanging idle

Check my thread. My issue ended being missing parts in the top of the carb coupled with poor quality fuel and vacuum lines. The lines were collapsing internally.

Quote from: sledge on February 05, 2011, 01:48:34 PM
I once had one pass through my hands that had a constant misfire and would drop a cylinder from time to time. Eventually tracked it down to the reg/rect earth. Look at the battery` -` terminal and follow the black lead away from the battery, 2-3 inches along is a spade connecter, make sure its clean and tight......it worked for me 

The easy way to check for poor earths is to connect a jump-lead between the `-` terminal and a clean metalic point anywhere on the bike. If the problem goes away you have got a bad earth.......somewhere.

aye. ive won a parts gs this way. guy said if i can get it to fire. its mine. i did in 10 minutes. using a spare set of jumper cables. had a bad ground somewhere in teh wiring mess of doom