Climbing idle. Running out of ideas. GS550L

[dkon777]

Hey guys I am in need of some advice as I am running out of ideas. I have a 1982 GS550L that I have been trying to get running properly. The bike fires up with no choke no problem (about 70 outside), and I can get it to idle around 1000 rpm. The problem is when I blip the throttle it usually will either hang or climb. I know this is usually an indication of an air leak or clogged carbs, but I have been beating those possible causes to death and am beginning to think it is something else. Here is a brief list of what I have done so far?
? new plugs, KN air filter, oil change, battery
? NEW carb to engine boots and NEW carb to airbox boots (with clamps)
? New intake boot o-rings
? Carbs completely disassembled and dipped. New o-rings installed.
Passages verified. Stock jets. Floats set properly. Bench synced to the best of my ability.
? Air filter box sealed with weather-stripping
? New NGK spark plug caps
? New petcock
? New vacuum line and fuel line/fuel filter
? Valves adjusted
? Compression tested when bike was cold and got good compression

That is all I can think of at the moment. Anyways, the bike will start no problem but the issue is with the climbing/hanging idle. I can adjust the idle knob on the carbs and get it back to around 1k, but about every 3rd time I blip the throttle it hangs and I have to mess with the idle knob again. As for the fuel/air mixture screws, I have tried them all at 3.5, 4, and 4.5 turns out with the same results. I even tried adjusting them individually to no avail. Like I said before the carbs were only bench synced so would that be the issue? Also, one of the slides in the carbs is SLIGHTLY more hesitant to come back to its stopping point than the rest, but it does indeed close without getting stuck. I am just trying to think of any possible cause.

I started buying the parts to do the coil relay mod today, and then I plan to go through the stator papers. Am I wrong in thinking this is still is a fuel/air mixture issue? I really do not think I have any more air leaks and the carbs could not possibly get any cleaner so I am stumped. Thanks in advance.

[Nessism]

My old 550 didn't run right until the pilot screws were out to 3.5 turns and a vacuum sync performed. You might consider giving that a go.

[tom203]

".....Also, one of the slides in the carbs is SLIGHTLY more hesitant to come back to its stopping point than the rest, but it does indeed close without getting stuck......"

With your CV carbs ,I'd be worried about this - I would think that engine vibrations help drop it back though. Are you sure your throttle cable ain't worn out internally and hanging up. Hard to check-so I probably just get new one ( if you haven't already) and rule it out.

[dkon777]

".....Also, one of the slides in the carbs is SLIGHTLY more hesitant to come back to its stopping point than the rest, but it does indeed close without getting stuck......"

With your CV carbs ,I'd be worried about this - I would think that engine vibrations help drop it back though. Are you sure your throttle cable ain't worn out internally and hanging up. Hard to check-so I probably just get new one ( if you haven't already) and rule it out.

Yeah I considered the throttle cable, and am planning to replace it, but I don't think it is the problem either. I have the bike on its center stand and blip the throttle with my right hand while holding the throttle cable where it connects to the carbs in my left hand checking for a stuck cable and it doesn't seem to be affecting it. But I do agree, it is best to just replace it and be sure...

[Guest]

tell us what "Bench synced to the best of my ability" comprises of...

[Tempted]

K&N filter. Pop your old stock one back in and see what happens. These bikes do not like high flow filters or pods without re-jetting.

[dkon777]

K&N filter. Pop your old stock one back in and see what happens. These bikes do not like high flow filters or pods without re-jetting.

You know I wondered about that. Unfortunately the PO put in the K&N filter so I don't have the original. You think that might be causing the hanging idle?

[Tempted]

Could be. My GS850 will not run correctly with pods. It will pop and crack, won't rev and the idle is extremely inconsistent. You can try taping up about 3/4 of the filter with some masking tape, then see if it makes a difference.

[dkon777]

tell us what "Bench synced to the best of my ability" comprises of...

I adjusted the carbs screws so that they were as close as possible by eye, then fine tuned it by using a small needle to put under each throttle valve until I got them as close as I could. When I was finished I could slide the needle to the exact same point under each throttle valve. I'm sure they weren't perfect, but I tried my damndest to get them as close as I could. I'm starting to wonder if it isn't that K&N air filter the previous owner put on the bike. Wish I had the original.

[tom203]

Add some deliberate slack to throttle cable- I set mine so I need about 10 degrees of throttle hand twist to get off idle stop screw.
When the throttle plates are in their idle spot, I can't see how a particular filter element would cause random idle hanging.

[Tempted]

Add some deliberate slack to throttle cable- I set mine so I need about 10 degrees of throttle hand twist to get off idle stop screw.
When the throttle plates are in their idle spot, I can't see how a particular filter element would cause random idle hanging.

The bike leans out. When a bike is running lean and you adjust the idle to fit it then as soon as it warms up the idle will jump. When you try to adjust the idle back down when its warm it won't run when its cold.

[koolaid_kid]

dkon, a bench sync is only for getting the bike running. You MUST sync the carbs on the bike once it is running.
Your symptoms are a classic lean condition. Use the procedure from the link in my sig to get your carbs synced and the lean condition will go away.
Best of luck.

[Guest]

I adjusted the carbs screws so that they were as close as possible by eye, then fine tuned it by using a small needle to put under each throttle valve until I got them as close as I could. When I was finished I could slide the needle to the exact same point under each throttle valve. I'm sure they weren't perfect, but I tried my damndest to get them as close as I could. I'm starting to wonder if it isn't that K&N air filter the previous owner put on the bike. Wish I had the original.

That bench-sync procedure sounds very good, just wanted to cross that off the list of possible issues.

As Tempted indicated, the K&N air filter may very well be the culprit. Also, some PO might have drilled a couple of holes in the airbox - check that too.

I don't have a lot of experience with the 8V 550, but I've worked on a couple of 16V 550's with the "funky" siamese carbs & neither would run right without the stock filter in the airbox. Perhaps the smaller carbs are super-sensitive to air flow, IDK, but when I replaced the K&N drop in it finally ran correctly.

As a test, cover the airbox inlet with a rag, rubber banded over the opening to provide more restriction - it that immediately helps then a new OEM filter is in your future.

[dkon777]

So a proper carb sync is probably my next move. I also plan to try to restrict some of the airflow to that K&N filter and see if that might be giving me issues. Thanks a lot for your advice guys it is much appreciated. One more quick question... Which carb sync tool should I buy? I see a lot of people recommending the Carbtune pro but its pretty pricey. Could I get away with using a cheaper tool such as one of these guys?

http://www.ebay.com/itm/MOTION-PRO-Sync-PRO-Carb-Tuner-Tool-Synchronizer-/180695911294?pt=Motorcycles_Parts_Accessories&hash=item2a1250cb7e&vxp=mtr

or

http://www.ebay.com/itm/New-Vacuum-Carburetor-Synchronizer-carb-sync-Gauge-CB-GS-KZ-550-650-750-850-/111211403960?pt=Motors_Automotive_Tools&hash=item19e4b75ab8&vxp=mtr

Also, do I need to purchase adapters?

[Tempted]

I built one for about 10 bucks in parts.