Project: 1985 GS550ES

I have a 1983 Nighthawk CB 700 SC that did the exact same thing you are describing. High idling. It would actually idle at 2,000 rpms when cold then shoot up to over 5,000 rpms and stay there. I could not figure out what it was and took it to a friend of mine who used a mannometer (sp?) to synchronize each carb. That did the trick. Each jet needle has to have the same vacuum pressure if my understanding is correct. There were 4 on my Nighthawk and there are 4 on my GS 550 E.

You might want to see if your carburator linkange is bent as well. OEM?

Airbox Boot Seal

Learned something new last night: Airbox boots are not permanently attached to the airbox. Wish I'd know that before. Live and learn.

When I pulled the boots from the air box I found that there was dried "something". Is this just "gunk" or is it the remnants of a sealant? If a sealant, what sealant should be used?

the high idle is from the either a carb boot leak or the pilot jets. When they're lean the bike will do that.

I was hopin' you'd have a chance to drop by. At this point I'm working on the air leak theory b/c a) it is such a prevalent issue and b) with the carbs recently cleaned (special attention on the pilot jets), it seems unlikely that their gunked again already.

Do you agree with my assessment of the plugs?

to be more specific - warm up engine - take screw out of boot closest to engine on one set of carbs - saturate with deep creep (loosen boot near air box saturate that end as well) then restart engine and stand back - it will smoke for a long long time (prepare to replace spark plugs if needed after this) , then do the same process for other set of carbs.

get your carbs adjusted/syncronized if it still idles high - one or two is out of sync.

Actually, the carbs are recently cleaned throughout. I believe the plug condition is a result of tuning issues. Do you agree with my read on the plugs?

[Nerobro]

the high idle is from the either a carb boot leak or the pilot jets. When they're lean the bike will do that.

deep creep

to be more specific - warm up engine - take screw out of boot closest to engine on one set of carbs - saturate with deep creep (loosen boot near air box saturate that end as well) then restart engine and stand back - it will smoke for a long long time (prepare to replace spark plugs if needed after this) , then do the same process for other set of carbs.

get your carbs adjusted/syncronized if it still idles high - one or two is out of sync.

Sea Foam Deep Creep

Hey there - get some seafoam deep creep from advance or autozone. Saturate your carbs (one at a time) and after saturation, restart and stand back (the smoke is normal). This will completely clean out the carbon (do this when engine is hot).

rinse, lather, repeat. You should see results immediately.

Spark Plug Reading

Here's a pic of my plugs:



According to the following images,

http://www.gnttype.org/techarea/engine/plugs.html

I'm thinking that the read is that my plugs are in the early stages of carbon fouling.

Would you agree?

Thanks for your time!

Is your throttle cable too tight so it's pulling on the carbs at rest?

Negative. I've added more slack than spec and checked to ensure that the throttle valve snap back all the way on the carbs when the throttle grip is released.

Is your throttle cable too tight so it's pulling on the carbs at rest?

If your bike is really warmed up, and it's completely off the choke but still has a high idle, then it's just a simple fact that your base idle setting is too high.

Have you tried to lower the basic idle setting?

If you're referring the idle set screw adjustment, yes. The set screw is backed off as far as possible.

And I still have no idea why the bike idles high after warm up. Anyone?

If your bike is really warmed up, and it's completely off the choke but still has a high idle, then it's just a simple fact that your base idle setting is too high.

Have you tried to lower the basic idle setting?

I read back a bit and found that you were thinking of replacing your boots, but it sounds like you haven't done that. There are o-rings on the underside of the boots where they meet the head. I recommend you at least replace the orings. Plus, switch out the philips head screws that attach the boots to the head for some socket head screws - you can get those boots torqued down better this way. You said you are using WD-40 to do your test for leaks. Try using Simple Green in a spray bottle - get everything dripping wet with the stuff while the engine is hot and running. Cover the boots, carbs, the whole area. This will give you more complete coverage than WD-40.

Countdown begins: 12 days until temp tags expire

And I still have no idea why the bike idles high after warm up. Anyone?

I'm still trying to think my way through it, but it seems strange to me that you can increase your idle by putting the choke back on when warm. It seems like putting the choke back on should just make it to rich. That's how it is on my 550. I would think this could only increase your idle when there's extra air availabe to mix with the added gas from choking. Are you sure your needles are set in the slides properly, and that your slides are seating correctly, and that all of the passages to your diaphrams are clean? I know you've mentioned that you didn't dip these carbs...I'm wondering if the vaccuum balance on top and below your diaphrams is somehow messing up with the added heat and pulling your slides up in the process. Just a guess though. And a kind of crappy one at that.

Can anyone else speculate on this issue?

Thanks LEESGS550E for your thinking cap time on this. I'm coming up empty on this thing except for speculation. I agree that it seems that there must be extra air coming from somewhere, but I can't seem to figure out where.

My understanding of the choke is that it meters both fuel and air (drawing fuel through the choke pipe from the bowl, mixing that fuel with air from the float chamber and then mixing that air/fuel mix with air again at the choke plunger and then porting that mix to the barrel after the butterfly valve). Therefore, I can imagine that the choke could introduce a lean mix IF there is a problem with the choke circuit. Of course, since the choke is designed to deliver a richer mix, if there's not a problem with the choke circuit then I would expect setting the choke to "bog" the engine.

I don't see any reason that there may be problems with the slides/needles or diaphragm pressures. The reason I didn't dip was that these carbs were very clean to begin with. Although I cleaned all passages, the only things that were actually in need of cleaning were the pilot jets and the choke pipes and the float bowls. Everything else looked pretty good. If these were at issue, wouldn't I see problems throughout the range of engine speeds and not just at idle? Plus, since I know the butterfly valve is returning to closed, wouldn't that minimize the effect of any issues with the main jet circuit?

I keep coming back to the though that my pilot screws are the culprit, and with two of them frozen, I'm thinking I'll have to get them drilled out to fix this issue. However, it seems, based on other posts that I've read on the topic, that the pilot screws generally won't vault the RPMs to 4000+.

The tough part of this is that I've only got until July 6th to fix this issue and get the safety inspection done before my temp tag runs out. The sad part is that this looks to be the only issue keeping me from getting the bike through inspection. Help!