List of causes for high idle?

[Guest]

My stage-0 (making up for decades of neglect and wear/tear/aging) is not quite complete, buuut....

I've got a high idle of about 1500. Not that high, but even with the idle knob almost removed, it's still too high.

My petcock diaphragm is leaking (new one is on its way, I'm going for a rebuild, everything else looks good).

The throttle tension adjustment at the carbs was set too high, and every time I put my throttle together, it pulled on the cable.

My intake boots have been sealed pretty well with silicone (I know, I know, new ones are on my list), but I can't detect any significant intake leak either at the airbox on either side, or at the head, or where the airbox and carbs meet. There might be a little leak, but I don't think there's much of a leak.
The intake boot O-rings are new.

So - finally my question. What all can cause a high idle? Is there a throttle plate stop screw I could have missed?

Obvious causes:
Something pulling on the throttle cable (not happening)
Intake leaks (don't think are happening, but it's hard to tell)
Excess fuel intake (like through a leaking petcock diaphragm)
Choke circuit sticking (nope)
Incorrect jets (stock jets, intake, exhaust, and airbox as far as I can tell)

I bench-synched the carbs, but I'm waiting to try to synch them with a home-made carb synch tool... once I figure out the idle.

What am I overlooking?
What else can cause a high idle?

Cheers

[Nessism]

You can lead a horse to water but can't make it drink...

[WilliamGLX81]

Neigh.

In other words, I'd love to replace the carb boots, once I can afford to. I'm broke, not cheap.

[Big T]

Air leaks

Air leaks

Air leaks

Idle screw too high

[Nessism]

Air leaks


Air leaks

Air leaks

Idle screw too high

...also

Pilot screws too lean

Air leaks

Air leaks

NO VACUUM SYNC

[850 Combat]

i have had a worn mechanical advance cause high idle on a different brand its probably air leaks though

[WilliamGLX81]

...also

Pilot screws too lean

Air leaks

Air leaks

NO VACUUM SYNC

A-ha! Well, I'd like to vacuum sync them. I'm waiting on the petcock diaphragm to do that.

See, I'm asking because I want to know if I should have a proper idle before I try to vaccum sync them.

Not responding to idle screw, pilot screws all set to 2 turns out.

I'll check the airbox side boots again tomorrow.

How many ways can the airbox leak?

[Nessism]

Set pilot screws to 2.5 - 3 turns.

Plug vacuum line and vacuum sync...after you get the new intake boots.

[WilliamGLX81]

Hmmmm. The air filter box on the parts fiche I'm looking at is rotated 90 degrees along the length of the bike. My airbox opening points out to the side, the fiche shows it pointing towards the sky.
That's weird, and my airbox seems to be attached how it should be.

[tom203]

The parts fiche is wrong on most sites. Make sure you get filter element or bike will run poorly even with those new boots that you will need.

[cowboyup3371]

And remember that Nessism is saying the intake boots - that's on the carb side not the airbox side. But it is still a good idea to replace both.

[WilliamGLX81]

Hmmm. Are the inside and outside plenum (airbox) boots supposed to be different lengths? Because mine are. And I can't get them to fully seat with pressure on them and/or the carbs any which way.

The airbox boots still seem fairly pliable, but yes... I do have an air leak on #4 carb holder/engine side boot. But there must be more than that, since even with the plug wire pulled off #4, it still idles up around 1100.

I absolutely hate pulling the carbs on this bike. It is a huge PITA, since the air(filter)box will not come out with the plenum in place, and the plenum won't come out with the carbs in place.

[tom203]

Yeah, its a PITA but think positively- once done right (clean carbs, decent boots) you might not have to do it again.

[WilliamGLX81]

Sprayed both starting fluid and soapy water in ridiculous quantities all over every seam in the intake system. No changes in idle speed or smoke or anything that would indicate a leak.

My homemade carb sync tool (which needs restrictors haha) showed that they were way off. I need to put the restrictors in them before I draw any conclusions from it though.

[tfb]

Forgive my ignorance, but do you have VM or CV carbies on your 650GL?

If VM's, I think it's possible to have all the slides raised too high, due to their individual adjustment screws (under the carbie caps) being screwed in too far.

Go to the carbie adjustment article for VMs (I think it's in the GS Resources 'Garage' section, from memory), and follow the instructions for a bottom-up rebuild for your carbies. That way you'll eliminate any other causes of high idle, besides <drumroll!> leaking intake boots.