2008 GS500 Hanging Idle - help?

[andrewtclarkson]

2008 GS500 - 18000km, bought from original owner (non running). It sat for a couple years, only got started up a couple times.

Cleaned up the carbs, threw in new plugs, got her running. New tires, chain, some other little things.

shaZam! in gas tank made it thru to carbs, gunked them up again, dirt in needle/seat, causing fuel to run all over shop floor. Put a filter between petcock and carbs, cleaned carbs, drained tank to remove all the crap, all is well again.

Checked valves (clearances good).

I put 2000km on her this year since purchase.

About 3 weeks ago, one for the mechanics at work mentions my idle seems low and the bike was kind of sputtering. My tach doesn't work (bike was laid down at one point) and I had not yet gotten to setting it just right. We raise it a bit, she runs awesome, feels like a totally different bike (it was way too low before, I'm not used to something that revs/idles this high).

Next day, I've got a hanging idle issue. I screw around with the idle speed screw, which leaves me with an idle that hangs high (4k ish I would guess) or nearly if you let it try to idle.

I put half a can of seafoam in the tank and went for a ride (140km), then it sat for a day, then took it to work (8~mins each way), seems to be running well.

Took it to work again today, back to hanging idle.

Been screwing around with her tonight trying to get this figured out.

Propane torch around all the lines, seems there are no vacuum leaks.

As per: http://gstwins.com/gsboard/index.php?topic=41199.0

0. Set idle when warm - check.
1. O-rings - this is not the same carb as seems referenced (http://www.mrcycles.com/oemparts/a/suz/508b0749f87002353072351d/carburetor-not-for-u-s-market I believe - #42 oring?) Correct me if I'm wrong, or am looking at the wrong parts! My carb is: http://www.mrcycles.com/oemparts/a/suz/506b3270f870022ba8af9a85/carburetor
2. Carbs have been cleaned twice - should I just tear them down again? The filter should be keeping them clean at this point.
3. Cables are all good.
4. No exhaust leak, valves are good.

Tonight I pulled apart the petcock, it seemed in order and clean.

I have not balanced the carbs, but the hillbilly balance check (remove one spark plug wire then the other) showed no major difference.

Because this issue seemed to appear after we raised the idle, I'm not 100% sure if it was an issue before.

Starting to pull out my hair a little here. Should I just tear the carbs apart again, or is there something I'm missing?

Thanks in advance!

[Jespenshade12]

Is the throttle cable ok? Frays may cause that issue. Just a thought

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[andrewtclarkson]

Yes, throttle cables are good. little bit of slack.

[andrewtclarkson]

update - balanced the carbs by ear and its 90% better. barely hangs. We'll see how she runs tomorrow!

[W201028]

Yes, balance the carbs. The hillbilly method you mentioned to check carb balance should only be used to check for a dead cylinder, whether it be lacking spark, air, or fuel. Balancing the carbs is to adjust the throttle plates to meet the demands of each individual cylinder. So, if one has wear and pulls less than the other, you open the throttle more to put more air/fuel in to compensate.
Motion pro sells a great balancing tool, its costs a bit, but like any other tool, it will pay for itself every time you use it. And paying a shop to balance costs more than the tool last time I checked.