07 was running fine, but now idles then dies, will restart if it sits for a few

[Philyhawk]

I bought an 07 gs500f 2 years ago with about 9k miles.  It was in decent shape. I changed the oil and filter, air filter, new tires, new pads, so on.  It had been running well and did about 3000 miles on it this past summer.  Right before winter, i gave it an oil and filter change and it still ran fine.  I filled the tank and put some fuel saver in there, hooked it up to the battery tender.  I turn it on every two weeks or so and let it warm up and idle for 15 to 20 minutes (i was told this is actually bad so I'll stop doing that.)  This past weekend it was nice so I fired it up for a ride.  After 5 or so min of idle, it slowly dropped from 1200rpm to 800 before dying.  I started it back up, same thing, revs drop down and it starts to die.  If I give it gas it perks right back up, but as soon as I back off the gas, it slows to 800rpm and dies.  Then it won't restart.  If I let it sit for 5 minutes, it'll start back up, run for 2 minutes and then die.  I also noticed the lights dim a little as the rpm goes below 1000.

So far, I dumped in a bottle of seafoam, pulled the carbs out and cleaned them (even though they were not dirty.)  Replaced the battery (it needed it.) It is still doing the exact same thing.  I checked all the vacuum lines, fuel lines, seals and anything I can see.  When it stalls, the battery is still reading around 11.8/11.9 so I don't think it is electrical. 

Last night I had a car mechanic buddy tell me maybe bad gas or bad fuel stabilizer and another buddy tell me to pull the spark plugs and look at them.  I don't think either of these things are it given that it starts right up with a little choke and runs for 10 to 15 min before the problem occurs.  I tried running with the petcock on prime and on reserve, no difference.  The only thing that changed between when it worked and when the problem started is that it is cold here in the northeast now and the added fuel stabilized? 

What can I trouble shoot next?

[mr72]

Will it stay running (better) if you keep the revs high? Like, don't let it try to idle?

If so, then that's precisely what mine did.

Do a compression test. If the compression is low, even on the very edge of the recommended range, then this running behavior coupled with the compression numbers indicate the valves are not sealing. Could be tight valves, which is easy enough to check. But if it turns out you have enough valve lash clearance and they are still not seating correctly then this could be carbon buildup or bent valves (or like mine, both), or maybe a burnt valve or damaged valve seat etc. Anyway, the solution is the same: top end rebuild.

[Philyhawk]

If I stay on the gas, i can keep the revs at whatever I want, but as soon as I back off the gas, it glugs and dies.  Compression test was just outside my abilities but I had a neighbor do it and he said it was fine?  I didn't ask high or low within 'fine' but it he didn't seem concerned.  He is retired and fixes lawnmowers for extra money and he is stumped on this one too.

[mr72]

Yeah compression on a car that's "fine" is maybe 120psi. 120psi on a GS500 is low enough to cause the issues you describe, minimum should me more like 140psi. Compression ratio is way higher on your GS than on a lawnmower

You need the number.

I bet you have a valve-sealing problem.

[The Buddha]

Sticking float comes to mind, and sitting = bad gas, always a worthwhile idea to drain carbs and start over with fresh gas.
Its not electrical, you're right about that. The thing smells like gas right ? then yea sticking float and likely a wet air filter.
Cool.
Buddha.

[Philyhawk]

The garage I keep it in is 20 minutes from my house and 20 minutes from the parts store.  I am going over there today but wanted to hit the parts store on the way.  The trips back and forth are eating up all my time I have to actually work on it.  at this point, I am going to replace the spark plugs just to rule them out.  I'll dump the gas and replace it with premium from a different gas station and not put any stabilizer in it.  What other things should I / Can I easily check off the list today?

[The Buddha]

Smell for gas around the airbox, and actually a nice ride with all the carb parts kostling about may be just what the doctor ordered.
Cool.
Buddha.

[The Buddha]

Yeah compression on a car that's "fine" is maybe 120psi. 120psi on a GS500 is low enough to cause the issues you describe, minimum should me more like 140psi. Compression ratio is way higher on your GS than on a lawnmower

You need the number.

I bet you have a valve-sealing problem.

Not likely. A tight valve will act up as it warms up. Not past the 5 min mark. Also a tight valve when its hot is more likely to show signs of being lean, than rich, though his symptom is a bit inconclusive.
A bike will need to be revved constantly 5 sec after start up and when you dont do that, it will abruptly die.
Cool.
Buddha.

[mr72]

The garage I keep it in is 20 minutes from my house and 20 minutes from the parts store.  I am going over there today but wanted to hit the parts store on the way.  The trips back and forth are eating up all my time I have to actually work on it.  at this point, I am going to replace the spark plugs just to rule them out.  I'll dump the gas and replace it with premium from a different gas station and not put any stabilizer in it.  What other things should I / Can I easily check off the list today?

Skip all of that and buy a compression tester at the parts store instead.

If you're going to work on it or check something, check the valve clearances. No reason to go to the parts store for that, since you'd have to order shims anyway after you do the measurements and math.

I know you really want it to be a fuel problem or a carb issue or an ignition issue. Maybe it is. But I'd not waste any effort on any of that until I knew what the compression numbers were. 140psi for each cylinder is a bare minimum. A lot of folks on this forum will disagree with my assessment here, but it doesn't hurt to check and be sure. It is not a difficult test to do at all, way quicker than draining gas. Basically the same as changing spark plugs.

It's not a fuel problem. Running at high revs and not at idle is not a "too little fuel" or "bad fuel" issue. Running at all rules out ignition. If it died when hot no matter what revs you kept it at then it might be the signal generator (ignition) but if it runs even a little bit at high revs when hot but will only idle when cold then I'm telling you it's the valves. Nothing else makes sense.

I hope I'm wrong, and I'm sure a couple of folks will come out of the woodwork to point it out. But to prove it you need a compression test. If I'm wrong, the cost is $20 for a compression gauge and 10 minutes of time, and for that you buy some peace of mind that at least the compression is good and Josh doesn't know what he's talking about. If I'm right then you may spend a lot of time and energy chasing your tail and trying to fix a bunch of stuff that's not broken only to find you have to yank it all apart and do it all again because the head and jug has to come off.

[mr72]

Not likely. A tight valve will act up as it warms up. Not past the 5 min mark.

Whatever, I'm tired of arguing about this.

Check the compression then you'll know.

Buddha, what's the point of talking people out of checking compression? I actually lived through this very problem on my bike so I have objective and incontrovertible evidence that non-sealing (I didn't say "tight") valves will behave exactly this way. In fact, the motorcycle I bought was one where the previous owner described these problems on this very forum and the forum members (perhaps even you!) also told him all the wrong things that it could be until he sold it to me without disclosing (or likely knowing) what the problem was, then I got here, everyone told me the same wrong things, I did everything to try and fix it until finally the shop did a compression test and when the head was off it was obvious the valves were bent. $900, a top-end rebuild and 3K trouble-free miles later, you know, I'm a believer.

[The Buddha]

Mr72 - Correct, bent valve isn't tight valve, a bent valve will not seal at all, so 5 min mark for tight valve, and till engine is rebuilt for bent valve.
However compression tester wont be able to test bent valve vs tight valve. A valve check with feeler gauge will could and better yet, it likely needs done anyway.

Cool.
Buddha.

[mr72]

Agreed. Compression test AND feeler gauge test will reveal bent valve vs. tight valve.

>0 valve lash clearance and bad compression: possible bent valve (given symptoms)
<0 valve lash clearance: tight valves, fix first then recheck compression (given symptoms)

Once valve lash clearance is established as good, if the compression is still bad it doesn't matter whether it's carbon, bent valve, worn rings, broken/stuck ring, etc., solution is the same: top end rebuild. Makes little sense to try and diagnose until the head is off, when it'll be obvious.

[gregjet]

Still think the needle/seat or the float is the problem most likely.
eg.The vacuum cutoff could be sealing ok but when it idles too much fuel could be flowing in raising the fuel bowl level and rich fluffing it. Stop it , the vacuum cuts off the fuel flow and the fuel evaporated enough to lower the level and it will start again, until the flowing fuel overfills the bowl. other similar scenarios possible.
OR vacuum isn't consistant enough to allow fuel flow at idle.

[mr72]

fuel flow at idle is not dependent on vacuum. It's dependent only on the pilot jet/passage not being clogged.

IDK about the fuel flooding thing, doesn't make sense to me. BTW this is what the shop that eventually did my top-end rebuild initially thought was wrong with my bike. They were wrong

[gregjet]

The fuel flow TO the carbs is dependant on the vacuum fuel stop in the tap unless it is on prime.

[mr72]

oh yeah, gotcha.

But that doesn't make sense with this issue, does it? Bike does when going down from high revs, the float bowls should have plenty of gas in them, it isn't being starved for fuel at idle. It'd have to idle a long time to deplete the float bowls and die (like a few minutes) before stalling that way if the petcock was not opening.

It could be the pilot jet/passage is COMPLETELY clogged or there's something clogging the pilot air orifice so the bike literally will not idle but that makes no sense about running ok before it's fully warmed up.

Could be a gross vacuum leak letting a LOT of air in, which is way too much at idle since it causes air velocity to go to zero over the pilot jet and the bike dies. That's the theory like the intake boot o-rings are gone or there's a crack in the intake boots. Or of course the pilot orifices are closed, same effect. But still, that affects it the same when cold as hot. In fact that might get better as the bike heats up because things expand so the vacuum leak tends to close up.

Just being fair, I'm really not absolutely clear on how/why bent valves/carbon buildup/burnt valve/etc. causes the bike to not run at idle when hot while not affecting its ability to run at idle when cold. Only way it makes sense is that when it heats up the gap where the valve doesn't seal gets larger and there's a point at which it's too large.  I suppose the reason it wouldn't idle when hot but would run at high revs is the same as why a lot of valve overlap works at high revs but won't idle: it's the exhaust valves that are bent or carbon-caked, so they never close all the way and exhaust gases leak in. Due to velocity, timing, intake vacuum and pressure, more exhaust leaks in per cycle at idle than at high revs, so the bike dies at idle. When the engine is cold the valve seals enough to prevent that critical amount of exhaust to leak in that would stall the engine. ??

I'm no mechanic. I'm just a guy who can read and who owns a motorcycle.

[Naptown]

Did you ever find out what the root cause was?  I have the same issue.

[Darkstar]

Are you testing on the center stand with fuel ON? Side stand with PRIME would cause your problem. Also, does it run smoothly and when's the last time you sync'd the carbs? Compression gauge would be smart to have anyway to approximate the health of your cylinders/valves, but I like to try everything else before I buy special tools.

[mr72]

Side stand with PRIME would cause your problem.

How is that?

[Darkstar]

Side stand with PRIME would cause your problem.

How is that?
[/quote]

PRIME pulls fuel with gravity so the left float bowl fills more than the right. I had identical symptoms as OP here when taking the bike out of storage, then I put it on center stand with ON, and it ran the way it should.