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List of causes for high idle?

  • Thread starter Thread starter WilliamGLX81
  • Start date Start date
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WilliamGLX81

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

In other words, I'd love to replace the carb boots, once I can afford to. I'm broke, not cheap.
 
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i have had a worn mechanical advance cause high idle on a different brand its probably air leaks though
 
Nessism said:
...also

Pilot screws too lean

Air leaks

Air leaks

NO VACUUM SYNC:eek:
Click to expand...

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?
 
Set pilot screws to 2.5 - 3 turns.

Plug vacuum line and vacuum sync...after you get the new intake boots.
 
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.
 
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.
 
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.
 
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.
 
Yeah, its a PITA but think positively- once done right (clean carbs, decent boots) you might not have to do it again.
 
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.
 
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. :D
 
CV I think. Mikuni BS32SS... Yep, wikipedia says they're CV.

PS I was just thinking about it - the air filter was not particularly oily (read - it felt almost dry to the touch). Should I oil it now or after I figure out the carb synch?
 
A good bench sync should have left carbs close enough so you could get a stabil 1200 idle (set with idle stop screw) to proceed with vac sync.If you still got too high an idle, too much air (likely leaky boots,clamps between carbs and engine) is to blame. You did put new o-rings on the idle/air mixture screws?
 
I had the same problem but mine was erratic idle. up and down it went. I finally resolved myself to spending the cash on all new intake boots and o-rings. Even when I put them on bench synced the idle was a problem until I synced them with my manometer. I also had to set my idle mixture screws at 2 3/4 turns out. Now for the first time in the 3 years I have had the bike it finally idles like a dream and runs smoother than it ever has
 
Now for the first time in the 3 years I have had the bike it finally idles like a dream and runs smoother than it ever has
Click to expand...
I hear ya... and that's the way it always seems to be, hey. We chip away at these problems bit by bit, until one day we can say that "finally" things are sorted! Few things are more satisfying than resolving a long term tuning problem. :cool:
 
You have had a BUNCH of hints and a few outright requests to check a few things in this thread, you keep shooting them down with one excuse or another. I believe tfb hit the nail on the head with the right idea, even though it was the wrong carbs. :oops:

Even with a "good" bench sync, I have seen one carb that was still open far enough to hold the idle speed higher than it should be. A vacuum sync will get them all adjusted properly and you will then understand what we are talking about.


Now, if you don't mind, give me some details on your "homemade carb sync tool". You admit that it needs restrictors, but give us some details on how it's made, there might be a flaw in the design that will prevent proper readings, which will only keep you wondering.
icon_shrug.gif


.
 
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