Project: 1985 GS550ES

[LeeGS550E]

Don't have much to add, only that my 550 seems to have a limit to how high the pilot screws will alter the idel. It may differ, as you well know, between our bikes since mines not in as good a shape and jetted/breathed differently. The pilot air circuit MAY be able to get enough fuel in their to increase the throttle that much, but it seems unlikely. Seems like she would run way too rich when cold if this were the case. I know its low mileage, but how is your valve adjustment?

[MelodicMetalGod]

Haven't touched the valves yet. I was planning on checking them after I got permanent tags. Could valve specs cause the high idle after warm up?

[MelodicMetalGod]

I meant could valves "out of spec" cause a high idle after warm up?

[LeeGS550E]

I don't honestly know...I just know that adjusting my valves made the bike perform better overall. It seems that bad valve adjustment can cause all kinds of strange problems...just read uncle mike's long thread about his idle problem...

Its definately a variable I would eliminate if it were me...its relatively easy to do.

[MelodicMetalGod]

Today's plan

Hunt down an air leak. Everything I've found in my searches for this problem (high idle after warm-up) seems to point to some kind of air leak. Several folks had told me during the carb cleaning that I should replace the boots no matter how good they seemed to be to ensure that I avoided this issue. Well, I still think the boots are in excellent shape, but I have to take some time an do some serious testing to be sure.

If I can't find an air leak are there any other possiblities or will that mean I just haven't found the air leak yet? Thanks for your assistance!

[LeeGS550E]

FYI, I've had instances where my chokes were not threaded in completely, and this let a little air in through the choke passage. Why they decided to make those threads out of plastic, I'll never guess. Check there while you're at it.

Good luck.

[MelodicMetalGod]

It really doesn't seem to be the boots. I've got WD-40 all over the boots and there's been zero effect on the high idle.

[MelodicMetalGod]

Pulled the choke lines and checked their function. All seems well. Suggestions as to what the next step should be?

[LeeGS550E]

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?

[MelodicMetalGod]

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!

[MelodicMetalGod]

Countdown begins: 12 days until temp tags expire

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

[LeeGS550E]

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.

[zig06]

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?

[MelodicMetalGod]

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.

[t3rmin]

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