1982 GS1100GK - Intermittent issue - Engine died today - Help needed

[MtnManCA]

Hello,

I have posted about this issue with my 1982 GS1100GK (~16,000 miles) in two separate threads a while ago. Something new happened today (engine died during a trip), so I am starting a new post to consolidate facts and hopefully find a solution.

1982 GS1100GK - 168 - 091221.jpg

The issue: occasional loss of power. Sometimes, typically once or twice for a couple of minutes during a ~100-150 mile ride, the bike accelerates poorly, shudders hard during acceleration. This happens only when the engine is warm. It happened during 45 degree F weather and also in the summer at 105.

I noticed that often when this happens, quickly opening the throttle wide leads to a sudden, jolt-like strong acceleration, like the engine was snapping back into normal acceleration mode. Often - but not always - I can continue my ride after doing this after an episode or two as if nothing had happened.

Today, in the middle of nowhere in the Sierra Nevada, not too far from Clovis, CA the engine died after running poorly for ~10 minutes.

I tried to start it again immediately after it died but it wouldn't start. After ~15 minutes it started up and I was able to ride the bike - engine ran poorly - for ~10 miles before it died again. It took another ~15 minutes before I was able to start it again.

Opening the gas cap (no hissing/vacuum) and setting the petcock to PRI did not help.

This scenario happened three times until I was finally home. On the last leg of my trip the engine ran as strong as ever, idled and accelerated like it should and it was a pleasure to ride.

I got this bike ~2 years ago and went through all systems from front to back. When it runs, it runs beautifully but this issue needs to be resolved.

The following things were done, related to the issue:

• carburetors were professionally cleaned and rebuilt
• valves adjusted and double-checked
• new air filter (K&N, slightly oiled), sealed air box
• new intake rubber parts
• tank is clean
• fresh gas
• new petcock
• new stator and R/R. Battery gets charged
• battery is ~2 years old, well maintained. Issue has happened also with brand new battery.
• all electrical connections were cleaned, including switches and ground connections
• replaced ignition unit, coils, leads and spark plugs
• I have NOT checked hot compression yet and the carburetors were only bench-synchronized. When the bike runs normally, it idles smoothly and accelerates strongly which makes me think that both compression and synchronization are close to where they should be.
• a hard-wired Volt meter shows ~13.9 Volts when the engine runs at ~3,500 rpm.

Any idea what could cause this erratic performance?

Fuel starvation? Petcock is new. All fuel lines and the vacuum line are new. No kinks. Why would this happen only occasionally? Running the bike fast over longer periods of time is possible, which, to me, does not point to fuel starvation.

Could this be an electrical issue related to heat? I replaced the entire ignition system with new parts. Issue happened before and after replacement.

The fact that the bike - with cold and hot engine - CAN run and accelerate smoothly and minutes later doesn't, puzzles me.

And why did it get worse today? The engine has never died before.

Thank you in advance for your input!

[Nessism]

My guess is either vapor lock from a bad gas cap or maybe a bad ignitor which malfunctions when hot. Sorry I can't be more definitive.

[MtnManCA]

My guess is either vapor lock from a bad gas cap or maybe a bad ignitor which malfunctions when hot. Sorry I can't be more definitive.

Thank you for your response. Opening the gas cap did not help. No hissing, no vacuum.

I installed an OEM NOS ignitor which didn’t help.

I still don’t understand why whacking the throttle wide open in many cases fixed the issue.

[oldGSfan]

I'd still not completely discount Ed's suggestion. In certain situations where vacuum is low and fuel consumption is high I've had fuel delivery probs. Long uphill in 5th gear at low RPM like 3500 (stuck behind traffic). Bike died, pulled over to check if I had a signal to call for help. Tried bike after 3 mins, fired up and no problems after several months. I'd call it 'vacuum' lock not vapor lock but that's a quibble, I always thought vapor lock was heat related.

Oh: edit - whacking the throttle open affects vacuum. Hint! Not that it increases vacuum, but maybe a 'jolt to the system' affects things as the bike recovers?

Can you think of any common things going on? Fuel level when it happened? Going up a long incline, or varied terrain, what RPM/gear, etc might help. Though you have certainly provided a lot of info, I am thinking that if you really dive into the situation's similarities a light bulb may come on. I just figured out a bad gasoline problem this way, plaguing two bikes in somewhat different ways - one dying with any throttle, one not revving out to redline. Different amount of bad fuel must have been the issue there, but both happening at the almost exact same time was the clue I needed.

On a car I've had the vacuum lock make the fuses blow, and you can hear the hiss. On a bike I wonder if just a couple seconds of not filling the bowls and if the seal is letting 'some' air in but not enough, it cures it... for now. What I'm saying is you may not hear a hiss. I think fuel is 10:1 over electrical. Electrical gremlins, considering how meticulous you've been, seem less likely - in my case they typically fail and stay failed, they never miraculously recover. Well, on an old British bike all bets are off.

It's a very frustrating thing to have such issues, I know I've had every manner of problem stranding me all over this land

[MtnManCA]

Thank you, Tom!

I will investigate the vacuum lead. Would you simply remove the rubber seal in the gas cap?

The issue occurred with medium to high fuel level in the tank (the fuel level rarely goes below that as my trips are only 80 - 150 long and I get gas in the middle of a ride).

It occurred at high and low speeds but yesterday the bike seemed to "die easier" at lower speeds/smaller throttle opening.

[salty_monk]

I would have guessed at the same... dirt moving around in the carbs, fuel starvation or the igniter going out. It's also worth checking your plug leads and coils again. One bike I had that displayed those symptoms had a loose wire at the coil & the boot was covering it (Dyna coils). Just some ideas.

[oldGSfan]

That may be a quick way to check and costs nothing, but maybe there's a way to ensure you don't slosh fuel on the paint while you ride, I don't know.

I took apart a cap to swap the lock cylinder a while ago, but don't remember checking into if or how the venting works. It's not hard to disassemble though, and maybe you can see if there is any blockage of the air intake passage or rubber hardened. On other caps I have seen it's a rubber flap that allows air in and contains the fuel.

Once in my young and dumb days, not to be confused with my now old and dumb days, I stuffed a ouiple shop rags into a CB750 tank and spray bombed the tank. I rode around and all was good until once in a while the bike would die. Side of road, check whatever I could with stock tool kit (not much) and then ride off. Well, you guessed it, one of the rags was floating around and would go over the hump and block the fuel flow. I dislocated my knee kicking myself in the a$$ on that one.

Another time I was going cross country in a Fiat 124 Coupe. which qualifies me as a masochist. It was late summar, 120 degrees out and I was climbing through long steep grades in Utah and the car died. I limped into a rest stop and twiddled the points. Hey, that fixed it! Off I went till the next hill and again it happened. I was so clueless but still figured out that the car had vapor lock, so I ran with the heater on full blast and that solved it. But after a particularly long stretch of uphill, I got out at the summit to enjoy the cooler temp, and the sole of my right shoe slipped off completely, having melted. Good times!

Thank you, Tom!

I will investigate the vacuum lead. Would you simply remove the rubber seal in the gas cap?

The issue occurred with medium to high fuel level in the tank (the fuel level rarely goes below that as my trips are only 80 - 150 long and I get gas in the middle of a ride).

It occurred at high and low speeds but yesterday the bike seemed to "die easier" at lower speeds/smaller throttle opening.

[MtnManCA]

Thank you, Salty Monk and Tom! Good Fiat story!

When it comes to the non-venting gas cap: I never noticed vacuum/hissing and opening it never resolved the issue, at least not right away. Even multiple starting attempts did not help after the engine died. I opened the cap when the bike shuddered slightly or moderately and also after the engine had died last weekend.

Is there still a chance that the gas cap is involved in the issue?

As soon as I have time I will go on a test ride to provoke the issue. In case the engine dies, I will remove one of the spark plugs and check if there is a spark. This time I will stay closer to home so I still have a cell phone signal in case the bike won't restart.

[Rijko]

The igniter has already been mentioned.

Measuring 12v supply to the igniter would be nice.
Less definitive but simple check : the starter relais is fed
by the same 'source' (RH handlebar switch).
Unhook the green/yellow wire from the relais and measure
voltage there on the female connector from the loom.

If low voltage there, good chance the igniter also
gets low voltage.

Edit : if low voltage, whacking open the gas causes higher
rpm and higher voltage so the igniter might just get enough
voltage to function properly.

[MtnManCA]

Thank you, Rijk,

I will check the voltage. What do you think could cause a temporary drop in voltage? Also, why does the bike typically recover from these episodes during a ride as if nothing had happened?

Armin

[Rijko]

These bikes are known for bad wiring.

Corroded connectors cause bad connection and higher amperage.
That causes heat, so some wires will be hard.
Also you will find the transparent connector sleeves turned brown
due to heat, that's a good warning they need some tlc.
And the plastic multiconnectors have the same issue.

The handlebar switches are usual corrosion suspects, too.
Usually they need to be cleaned inside.

All these bad connections cause higher amperage, lower voltage.
This may result in broken electrical parts like regulator/rectifier.

During a ride, due to vibration sometimes connections are intermittent.
With corroded connectors that is.

Now this may not be the cause of your issue, but cleaning connections
is something that is important.

[Rijko]

In my experience, electronic ignition suffers when voltage drops below 10 volt.
It may not work at all suddenly and will resume function when enough voltage gets through.

Also i would not dismiss a broken igniter.
If an R/R breaks, often you get high voltage on the bike.
This may damage the igniter which will slowly get worse even
if the issue is corrected with new R/R, stator, etc.

Recently i had one on a GS450L i was working on :
the bike would run for half an hour at first and then get issues.
A week later it would run perfectly below 4000 or 4500 rpm ;
but would not rev well above that and it felt like a bad 250cc.

[Grimly]

These bikes are known for bad wiring.

Corroded connectors cause bad connection and higher amperage.
That causes heat, so some wires will be hard.

No higher amperage than normal, in fact slightly less in all probability, because of the high resistance of the corroded joint.

[Gorminrider]

Turn tap to Prime and see if that fixes it. I've had similar to ' OldGSFan (post #4)....opening the throttle lessens vacuum but snapping it shut increases it a lot momentarily... and sucks that petcock's valve out of its stupor.

[MtnManCA]

Issue resolved?

Thanks again for all your input! I focused very much on fuel starvation. Removed the tank, tested the petcock in all three positions and it worked well, good fuel flow.

Started the bike without fuel supply to empty the float bowls. Reconnected tank, put petcock in PRI position. Did not see any fuel flowing in the clear fuel line.

Removed tank again, thoroughly followed fuel line and saw it was kinked!! Rerouted and shortened it. Put petcock in PRI position again and this time I saw the clear part of the fuel line filling up with fuel.

Took 70 mile spirited test ride close to home in a cell phone reception area. Bike ran flawlessly and strong. First ride without any hesitation!

Will do another test ride soon to confirm things and regain confidence in the reliability of this amazing bike.