Bike randomly died while riding.

[stossboss_gaming_and_news]

So I noticed my bike randomly start struggling as I was about 3 miles from my house, barely accelerating downhill. It died as I pulled over to what used to be a motorcycle mechanic shop (that would have been great but they moved a few months ago). Any GS wizards have something similar happen to them?

Unfortunately I have not yet devised a roadkit so I wasn't able to check anything really. Regular and bump starting it would try but stumbled off everytime.

My theories -

Fuel, possibly a clogged filter? The hoses were not kinked.

Electric -

Ignition coils, battery, and spark plugs are new, the only part I really cheaped out on was the r/r (caltric crap) because at that point I wasn't prepared to fork out $150 on a bike I wasn't even sure ran well.

Background on electric problem. After running the bike for a respectable distance and letting it sit for 20 minutes, it would start on the first 2-3 attempts but if it died then nothing, like no juice was making it to the starter and it wouldn't engage properly. Only thing that would fix that was jump or bump starting or if I let it completely cool down, I had better chance of starting it. Weird issue, I thought the battery was overheating so thats why I got the r/r. Worked good for a few weeks but on one cold night the problem returned.

I plan to go back with my tools, jumper cables, and starter fluid, to determine if it's fuel delivery vs electric. If it is indeed electric, could a bad r/r cause the bike to stop firing properly mid-ride like that?

Put 600 miles on it in the last few weeks and it was working beautifully up until today!

 

[rphillips]

Hopefully fuel, did you put it on PRI for 4 min. then give it a try

 

[stossboss_gaming_and_news]

Hopefully fuel, did you put it on PRI for 4 min. then give it a try

Had it on pri for about a minute but no luck

 

[chuck hahn]

Does it have gauge lights? Actually has power when key is on? I would fully charge the battery and start it then put volt meter on battery to see if its charging or not. Low voltage can cause coils not to fire. If no dash power start checking connections and wiggle the lead going into the ignition switch. I had a 77 750 that i had to resolder the red lead as it was loose and would lose contact now and then.

 

[stossboss_gaming_and_news]

Does it have gauge lights? Actually has power when key is on? I would fully charge the battery and start it then put volt meter on battery to see if its charging or not. Low voltage can cause coils not to fire. If no dash power start checking connections and wiggle the lead going into the ignition switch. I had a 77 750 that i had to resolder the red lead as it was loose and would lose contact now and then.

I got back to it today but forgot my starter fluid... Voltage was 12.6. Bowls had gas.

4 things I noticed -

Airbox was a little loose, possibly leaking.

oil present in the airbox coupler, I guess overflow from the breather, is that normal? Not excessive but it is noticeable.

One of my mounting bolts from the fusebox frame to the bike's frame went completely undone, possibly not tightened well, it was lodged somewhere in the bike and put back in.

cam cover screws were a little loose but I don't think thats really relevant.

Anyway going back now and if I still cant get it started I guess I'll walk it home for 3 miles on incline...

 

[tom203]

Yes, charge battery and start bike to determine if it’s actually charging. …your shunt r/r might have fried the stator. The electronic ignition is sensitive to voltage drop off without much warning

 

[Grimly]

If it dies suddenly then 99% it's the main or ignition fuse (or one of the connectors to and from them).
Fuel problems tend to splutter before dying.

 

[rphillips]

Naw Grim, don't think it died suddenly, said bike started struggling and barely accelerating and finally died when he pulled over. That's why I's thinking fuel.

 

[stossboss_gaming_and_news]

Tried with starter fluid and connected to my car battery. Wouldn't start, tried putting the old r/r back on and same deal. Also noted spark was present in all cylinders, blue + orange, petcock operational, no kinked hoses, fuel was present in the bowls.

I guess next step is a compression test. Someone walked up while I was working on it and I explained everything I checked and he said the same thing happened to him and it ended up being compression related. Bike has 22k miles but did not receive the best care in that time so it's certainly possible I just would have expected a more gradual demise. My brother has the tool for that so I'll check it out tomorrow and if good then at least it's home and I can take a longer look at electrics and fuel delivery. It had been working beautifully up until yesterday and now I have the itch to ride :chargrined:

Ended up taking the tank off, walking it home 3.2 miles, 600 feet elevation - just grateful I had no incidents on the bike or while walking it and the caliper was rebuilt and not sticky!

 

[chuck hahn]

In that 22000 miles have the valves been adjusted? A compression test will be faulty if valves are tight and hanging open. Youll see low compression but that may just be valves need adjusted. I would visit a valve adjustment and then do a compression check knowing tight valves have been eliminated already.
If all the valves are good and it still shows lower compression do a leak down test. Roll each cylinder to TDC and take off the oil fill cap. Listen to the exhaust for exhaust valve leaks, carbs for intake valve leaks and oil fill hole for rings.

Go here and see if theres a service manual..............BikeCliff's Website​

 

[stossboss_gaming_and_news]

In that 22000 miles have the valves been adjusted? A compression test will be faulty if valves are tight and hanging open. Youll see low compression but that may just be valves need adjusted. I would visit a valve adjustment and then do a compression check knowing tight valves have been eliminated already.
If all the valves are good and it still shows lower compression do a leak down test. Roll each cylinder to TDC and take off the oil fill cap. Listen to the exhaust for exhaust valve leaks, carbs for intake valve leaks and oil fill hole for rings.

Go here and see if theres a service manual..............BikeCliff's Website​

Yeah valves was initially probably the biggest problem, adjusted them to spec about 2 months ago. Thanks for the other suggested tests if compression really shows a problem I'll update when performed.

 

[chuck hahn]

If you hear a low hiss from oil cap thats rings. but IF ITS a rather heavier louder type hiss i would suspect an actual holed piston. How do the plugs look? any really white lean looking?

 

[Griffin]

I had an '81 GS750E that ran great, but every once in a while, it would suddenly start sputtering, lose most of it's power, and die. I'd let it cool off for 10-15 minutes, then it would start right up again, and run down the road just fine for a while.

It drove me and one of our other resident GS gurus crazy for a month. Figured it had to be a fuel issue, the way it lost power.

Turned out, it was the one and only stock coil I've ever had go bad on me. The coil would heat up, and then stop firing it's two cylinders. Once it cooled off, it worked fine.

Turned out to be a super simple fix, but was a bear to find.

 

[steve murdoch]

I had an '81 GS750E that ran great, but every once in a while, it would suddenly start sputtering, lose most of it's power, and die. I'd let it cool off for 10-15 minutes, then it would start right up again, and run down the road just fine for a while.

It drove me and one of our other resident GS gurus crazy for a month. Figured it had to be a fuel issue, the way it lost power.

Turned out, it was the one and only stock coil I've ever had go bad on me. The coil would heat up, and then stop firing it's two cylinders. Once it cooled off, it worked fine.

Turned out to be a super simple fix, but was a bear to find.

Had the exact same thing on a '78 GS1000.
If i took the same route to work it would happen very close to the same spot on the highway.

 

[Griffin]

Had the exact same thing on a '78 GS1000.
If i took the same route to work it would happen very close to the same spot on the highway.

The OEM coils on the '70s-'80s UJMs are very robust and reliable. Failures are extremely rare.

Which is one reason why they can be hard to troubleshoot, because they aren't part of the "usual suspects" group of issues with these bikes.

 

[1978GS750E]

I had an '81 GS750E that ran great, but every once in a while, it would suddenly start sputtering, lose most of it's power, and die. I'd let it cool off for 10-15 minutes, then it would start right up again, and run down the road just fine for a while.

It drove me and one of our other resident GS gurus crazy for a month. Figured it had to be a fuel issue, the way it lost power.

Turned out, it was the one and only stock coil I've ever had go bad on me. The coil would heat up, and then stop firing it's two cylinders. Once it cooled off, it worked fine.

Turned out to be a super simple fix, but was a bear to find.

I just had the same thing happen to me on a '82 GS1100E while out in Missouri. Started missing occasionally one morning, cleared up until the afternoon. Felt like it had bad gas to me so I added some fuel treatment and it ran good for another 1/2 day. Until it wouldn't! I cut my trip short, replaced the bad OEM coils and now it runs perfect!

 

[rphillips]

Agree with Griffin, I never remember me nor any of my riding buddies ever having a coil problem... My "83" 1100E has those yellow Accel coils and wires that previous owner put on, he probably thought they'd give him more HP as many folks did. I'd feel more comfortable and it'd look better if it had orig.

 

[alke46]

I I'd let it cool off for 10-15 minutes, then it would start right up again, and run down the road just fine for a while.

This is such a sure fire sign that the coil/coils are bad. I learned this lesson many many years ago as it happened to me on more than one occasion, starting in my teenage years

 

[stossboss_gaming_and_news]

If you hear a low hiss from oil cap thats rings. but IF ITS a rather heavier louder type hiss i would suspect an actual holed piston. How do the plugs look? any really white lean looking?

All the plugs were dry and black, memory can be hazy so I'll share a pic tomorrow.​

I had an '81 GS750E that ran great, but every once in a while, it would suddenly start sputtering, lose most of it's power, and die. I'd let it cool off for 10-15 minutes, then it would start right up again, and run down the road just fine for a while.

It drove me and one of our other resident GS gurus crazy for a month. Figured it had to be a fuel issue, the way it lost power.

Turned out, it was the one and only stock coil I've ever had go bad on me. The coil would heat up, and then stop firing it's two cylinders. Once it cooled off, it worked fine.

Turned out to be a super simple fix, but was a bear to find.

Sadly I already replaced both coils on this bike this past year, so Im hesitant to put my thinking there, and it had the same (definitely separate to my current one) hot start issue with the older coils. Sort of felt like the starter wasn't getting any juice till everything cooled down. I do have one thick snipped ground cable on the top of my crankcase and I have always wondered if it's related, but in the diagrams I cannot find what it's used for as I the only one similar to it goes to the battery, also connected to a diff bolt nearby.

 

[stossboss_gaming_and_news]

Did the compression test today... All in the range of 55-65 PSI, engine was cold as it wasn't running. Just no idea why it's so low. Could timing be an issue?