Okay.

Today we planned to go on a longer ride. First up was to ride to my dad's house which is about a 15 minute ride away. Maybe 8 miles? Longest ride in one shot I had done before was maybe 4-5 miles.

The bike ran great for most of the ride there and then it started to sputter at low rpms (below like 5K?) and then it didn't want to run at those lower revs and then within about two minutes it flat out died. Wouldn't start back up. It seems it didn't want to run at all at lowish revs.

My dad came by and I double-checked the idle mixture just in case and by that time I guess it had cooled off enough that it started up and ran fine. But right around the time I got to his house, about maybe 2 miles later, it started to act up. I decided to go back and reset the idle mixture on both carbs to 2.5 turns out, just in case I had screwed it up. The bike started and tried to idle at like 4K rpms. I reduced the idle where it was supposed to be and it seemed to be running fine if not a hair lean showing with a touch of hanging idle. I bumped the mixture screws out to 3 turns which is where I've been running it for the shorter rides over the last week and it seemed to run fine. By the way, when it was running like this, giving it choke would cause it to rev higher. I surmise either a) it was not fully warmed up or b) it's running lean.

We took off to go on the ride and got about a mile down the road before the GS started to die again.

I was sitting at a stop sign waiting to turn and if I let the revs below about 7-8K it would try to die and when I turned the throttle to keep it from dying it would backfire intermittently and then run if I revved it like a madman. I turned around and hoped to get back to my folks' house before it would die altogether but no dice. A stop sign midway did me in. It died as soon as I put the clutch in to stop and would not start back up. I pushed it the 2 blocks back to the house.

We trailered home and it wouldn't start at the house either but I have a hunch it's because the battery is low, not enough to get a good spark.

I pulled the plugs when I got the bike home expecting them to be soot black but on the contrary they were gorgeously tan but with carbon around the base of the plug. Electrodes were tan. Looks like it's been running perfectly.

Okay. So experts, I need your help. The symptom is: the bike starts and runs fine for 10 minutes and then it won't run below 5K or 7K rpm, backfires when trying to keep the revs up while stopped. Let it cool for 10-15 minutes and it'll start and run fine again until it warms back up.

Carbs are jetted 40/127.5 bike has stock airbox and Yoshimura "slip-on" equivalent. Mix screws three turns out. Plugs look good but have carbon around the base. Ideas? Help?

Thanks!

Did you try setting the petcock on prime?

I don't suspect bad mix, I suspect lack of fuel.  Either floats/needles gummed up and slowing fuel intake or petcock on the way out.

Yeah I tried running it on prime. No difference. And it just doesn't make sense to me that the float level or needles would have a temperature-dependent behavior, especially one where it doesn't want to run at low rpms. Wouldn't poor fuel delivery cause it to not run at HIGH rpms? Again, when it gets good and warmed up, it will basically run normally at more than 7K rpms and is a disaster below 7K rpms. The main problem is it dies when you put the clutch in and won't "push start" itself when you let the clutch out if you are going slowly enough that it won't turn 7K+ rpms in 1st gear.

Does this sound like the signal generator going bad?

If so, can someone recommend a definitive way to test? Maybe measure resistance on the pickup coils while hitting it with a heat gun?

Have you checked your valve clearances?

Quote from: qcbaker on October 08, 2016, 03:21:45 AM
Have you checked your valve clearances?

No but this issue sure doesn't sound like it could possibly be valve clearances.

I am about 90% sure it's the pulse/signal generator(s). I guess the bad news is that it will take 2 weeks for me to get parts here. The good news is, well that gives me tons of time to check the valve clearances just so you guys will stop asking me.

Quote from: mr72 on October 08, 2016, 06:29:14 AM

Quote from: qcbaker on October 08, 2016, 03:21:45 AM
Have you checked your valve clearances?

No but this issue sure doesn't sound like it could possibly be valve clearances.

I am about 90% sure it's the pulse/signal generator(s). I guess the bad news is that it will take 2 weeks for me to get parts here. The good news is, well that gives me tons of time to check the valve clearances just so you guys will stop asking me.

Only reason I asked is because I know the valve clearances can sometimes cause issues that occur only after the bike warms up and they expand slightly due to heat.

Let us know if the pulse sig generator fixes it!

Quote from: qcbaker on October 08, 2016, 11:51:34 AM

Quote from: mr72 on October 08, 2016, 06:29:14 AM

Quote from: qcbaker on October 08, 2016, 03:21:45 AM
Have you checked your valve clearances?

No but this issue sure doesn't sound like it could possibly be valve clearances.

I am about 90% sure it's the pulse/signal generator(s). I guess the bad news is that it will take 2 weeks for me to get parts here. The good news is, well that gives me tons of time to check the valve clearances just so you guys will stop asking me.

Only reason I asked is because I know the valve clearances can sometimes cause issues that occur only after the bike warms up and they expand slightly due to heat.

Let us know if the pulse sig generator fixes it!

I do agree about checking valve clearances.  I've had bikes behave exactly like you're explaining.  I ended up having 9 out of the 16 valves (this was a 4 cyl) showing very low tolerances.  Adjusted then and sync'd the carbs, and no more dying problems or having to rev the bike to the moon to get some motion.

Quote from: Arpee on October 09, 2016, 04:00:05 PM
I've had bikes behave exactly like you're explaining. ...no more dying problems or having to rev the bike to the moon to get some motion.

I don't disagree it's a good idea to check the valve clearances but this is not at all the problem I am having. On mine, it will not run at all at low revs, like below about 5K rpms, once it's warmed up fully. It's not that you have to rev it to get it to go or it runs poorly or rough, it's that it flat-out dies dead if you let the revs drop below about 5K and it won't start again. Up until it is fully warmed up it runs and operates fine.

...

So I spent a little time yesterday debugging it. At first I thought it might be the signal generator (little pick-up coils under the right-side cover). The theory is there may be a break in one of the coils that only open-circuits when it is hot. This is actually a pretty routine failure of coils in general so it made sense. So I measured the cold resistance of each coil and they were both within spec (about 280-285 ohms). Then with the multimeter connected at the connector, I measured the resistance of them in series, just because it was an easy way to connect the meter and measure both at once, and then I used a heat gun to slowly heat up the coils. Over about 10 minutes eventually the resistance of each coil went as high as close to 500 ohms but neither would open-circuit.

Then I decided to run the bike and let it run in my driveway until it started acting up. I planned to check these coils for resistance again once it began to misbehave. I used the choke and then adjusted the throttle cable at the throttle end to keep it up around 3-4K rpms for like 10 minutes or so and then it started acting funny. The whole time it had a pretty regular misfire that was moderately troubling, but it finally started doing its thing. Under controlled conditions (not trying to ride it on the road) I was able to better observe the behavior. It didn't "just die" like flipping a switch as it had seemed to when riding on the road. Instead, it began to want to stall at idle, but it'd keep running if you caught it with the throttle and didn't let it idle. Then eventually it got so that it was really slow to rev off idle, sputtering a lot. Then it got to where if you let it go below about 3K rpms then it would not rev above maybe 2K sputtering the whole way even WOT. And finally it just simply died, since I was not willing in the driveway to run it at 7K rpm the whole time. It wouldn't start back up. There was a noticeable fuel smell when it died, which I hadn't noticed when it died on the road I guess because I was still rolling and I coasted to a stop in a parking lot like half a block away.

While in this dead state I thoroughly checked the resistance of the signal generator and it was like it was when heated with the heat gun... each coil like 480 ohms. Not the problem. I checked the ignition coils resistance, which was high both on primary and secondary (one primary alarmingly high, 11 ohms) but they seemed to be good. I pulled each plug and checked it. Both were black, one was wet with fuel. I checked for spark by putting the plugs in the boots and turning the starter with the plugs grounded, and both sparked fine. So I ruled out ignition.

I went to double-check my idle mixture settings and noticed fuel had been dripping from the left carb. Looks like it's dripping fuel from the idle mix screw (AGAIN!). That, and the fact that the left plug was wet with fuel makes me think maybe that idle needle o-ring is leaking. Today I'm going to try and find replacements locally and see if that fixes it. That's my current theory. It's possible it might be more wrong with that carb than just this o-ring, like maybe the float needle sticking (it was before, but I changed the needle and seat) or bad float in some other way, but I'm going to start with the thing that doesn't require pulling the carbs and see if that eliminates at least the fuel leaking.

My initial impression when it died on Friday was that it was running way rich on the pilot circuit, and when it got fully warmed up it was just too rich to run on pilot, so it would only run on main. That's why it wouldn't run at low revs or low throttle openings. If I have a leaking pilot needle o-ring then that would definitely cause a super rich pilot condition, and the fact that both plugs were black, and the left one was wet, seems to confirm this. I actually think it died not because of rich running, but because of a fouled plug. And it eventually re-started Friday after it cooled a few minutes and the fouled plug dried. I think it will run, but poorly, on the pilot jet, as long as the plug doesn't foul, but it dies once the plug gets fouled.

So I still think the problem is carburetor-related. It's a good-news-bad-news thing. Good news that I don't have to pay $165 for a new signal generator, and I know a lot about working on the carbs by now. Bad news that I hate working on the carbs and they make me want to set the motorcycle on fire.

And just so you guys will lay off ... I have a "new" tank on the way. Once it gets here and I pull everything apart to paint & swap, I will check the valve clearances. I have a whole mess of shims from my Miata wrenching days so I probably can get it dialed if one or more valves are off. Then we can put that issue to bed.

Based on your debugging, I definitely agree with your theory. Based on the evidence, it seems perfectly reasonable.

I think its worth it to check the valve clearances when you swap your tank, but I don't think any of your problems are related to that.

Hit the pickups with freezer spray when the trouble starts.

Quote from: sledge on October 10, 2016, 09:54:04 AM
Hit the pickups with freezer spray when the trouble starts.

That's an awesome way to crack a perfectly good part.

Stick around and you will see lots of bad advice given out in here, not as bad as it was but it still happens but you wont see it from me.

Now you can do this the easy way or the hard way...,..your call 

Quote from: sledge on October 10, 2016, 12:27:05 PM
Stick around and you will see lots of bad advice given out in here, not as bad as it was but it still happens but you wont see it from me.

Now you can do this the easy way or the hard way...,..your call 

Dude, are you like going out of your way to sound like a jerk? If you're trolling, then sure whatever I guess, but you've replied to like 3 of mr72's posts with barely anything constructive to say. If you actually have anything worthwhile to add, then add it. Otherwise, you're just coming off like a pompous jerk.

Another relative newbie

Quote from: sledge on October 10, 2016, 12:46:29 PM
Another relative newbie

So, your reason for being a jerk is that he/I joined the forum more recently than you? Why would you just assume that other people don't know what they're doing just because they haven't been a member here for as long as you?

I'm not trying to derail this thread with an argument, I'm just genuinely curious as to why you're acting like this.

A tip for the newbies, including yourself   

If you want to get the most out of this forum, focus on what is being said rather than who says it.


Now I am waiting for a really interesting discussion on 'solid state' motorcyle ignition systems to start. Particularly how to overcome pickup/control circuit compatability issues.

I fixed the leaking o-ring on the one bad carb and now it doesn't leak. But the problem persists.

In 10 minutes running in my driveway I was able to get it to act up. Won't run below 5K rpms, backfires and sputters if you let the revs drop below 5K, etc. Happens all of the sudden pretty much after running beautifully for 9.9 minutes Eventually if you accidentally let the revs drop it will die and won't re-start until it cools.

I pulled the right side cover and measured the coils resistance when it was acting up. One is 271 ohms and the other climbed significantly to 480 ohms from about 285 where it is when cold. Still neither are open circuit so it doesn't seem like this could be the problem. But I am not ruling out ignition altogether.

Why does there need to be an open circuit for them to be faulty?

Quote from: sledge on October 10, 2016, 11:42:15 PM
Why does there need to be an open circuit for them to be faulty?

That's the failure mode of a broken coil. When heated, the coil and everything in it expands, which may pull open a crack in the wire and lead it to open-circuit, which would result in no pulse being generated. When it cools back enough to contract and the broken wire ends to make contact, then it measures normally.

There's no other reasonable failure mode for the pickup coils in the signal generator, not one that would not negatively impact the series resistance. I already verified all of the other wiring all the way to the igniter, and verified that even when hot and failing it still produces a spark. This should rule out ignition.