Hello, when adjusting the carb idle mixture, what does it mean if there is no rpm change for any screw turns? My left-side carb runns exactly the same rpm whether the screw is all the ways in, or 3-4 turns out. (Right side seems to like it around 2 turns out.) Plugs indicate med on r side & dark/black on l side. Was trying to correct for back fire & slighly hanging idle when hot. Tried leaning out l-side with vac gauge & tach and no difference for the first 3-4 turns out. Could this be indicative of a problem?

Sticking float?
Needs carb cleaning?
Side stand lean? (No center stand)

Leaking/shot o ring on the idle mixture needle.

I've been meaning to ask the same question.

I've not ridden many other GS to compare, but have always been happy with how mine rides.  My plugs look a healthy tan, so think overall mixture can't be too far out of whack.

I have tried fiddling with the air mixture screws to see if I can pick up any more performance, but tweaking them never seemed to change RPM at idle.

I recently rebuilt the carbs as I was having some hesitation pulling past 5000rpm in 4th or 5th gear.  That's somewhat better.  But on the air mix issue, new O-rings on the mixture needle, and still no difference.

Baseline idle screw it set to keep it about 1200rpm after well warmed, choke off.  Another other thoughts?

Quote from: Endopotential on October 13, 2017, 11:31:41 PM
I've been meaning to ask the same question.

I've not ridden many other GS to compare, but have always been happy with how mine rides.  My plugs look a healthy tan, so think overall mixture can't be too far out of whack.

That's because you are riding on mid and main jet most of the time. Plugs are not going to indicate idle mixture.

Quote
I have tried fiddling with the air mixture screws to see if I can pick up any more performance, but tweaking them never seemed to change RPM at idle.

....  But on the air mix issue, new O-rings on the mixture needle, and still no difference.

Baseline idle screw it set to keep it about 1200rpm after well warmed, choke off.  Another other thoughts?

In your case I think the next thing to check is if the pilot air or fuel passages are blocked, clogged or obstructed. If the pilot mixture needle adjustment doesn't have an effect then for some reason the pilot jet is not supplying fuel. So maybe your air filter is blocking the little hole that the idle air comes through, or it's clogged, or the fuel passage beneath the pilot jet is clogged or the pilot jet itself is clogged ?  In other words you may be idling on the middle jet with air coming past the throttle plate. If it's a steady reliable idle and you have no other running issues then I wouldn't worry about it.

So getting back to the op, if there is no change/adjustment in one of the mixture screws, it could be a bad o-ring or dirt? I'm pretty sure there isn't an o-ring (just pulled screws out of extra carb) but dirt/debris is a definite possibility. I've had problems w/tank sealants getting into the fuel line.
I'll check it out.

Quote from: 1034am on October 14, 2017, 06:33:10 AM
So getting back to the op, if there is no change/adjustment in one of the mixture screws, it could be a bad o-ring or dirt? I'm pretty sure there isn't an o-ring (just pulled screws out of extra carb)

Sometimes (maybe usually?) when you remove the needles in an old carb, the o-rings don't come out with them. I found with my carbs I had to pick the old o-rings out with a piece of bent wire. Is there a chance you swapped the needles ("adjustment screws") but didn't get the o-rings and/or washers out?

I still say the chances are that o-ring is leaking. Unless you explicitly replaced it with a brand new one, it's 99% likely to be leaking. Especially since the symptom is exactly the leaking o-ring symptom.

[/quote] but dirt/debris is a definite possibility. I've had problems w/tank sealants getting into the fuel line.
I'll check it out.
[/quote]

Can't hurt to check but far and away the odds are a bad o-ring. You can pull the pilot jet out and run a wire through the passageway to help clear it. Also you need to clean/clear the pilot air inlet on the carb throat, especially if you ever ran an oiled air filter or ran with no filter or poor-filtering filter (i.e. K&N etc). If that gets clogged then you won't ever run on pilot at least on that carb.

My vote is still that o-ring. I had so many problems because of these o-rings.

Where do I find the air inlet on carb throat? The slots along side where air filter connects? Because...I did recently oil the filter (which fits the timeline of problems.)

Yeah it's those slots AFAIK. I'm no kind of pro with those carbs.

Good call on the idle screw o-rings: they were very calcified. I cleaned them up & reinstalled (while I wait for the new ones.) Bike ran much better (still had slight hanging idle, but back-firing was much better.)
One problem I found, however, the seat on the problem/left side had stress cracks. (Other side was good.) There are probably 2-3 little hairline cracks where the o-ring meets the seat.
Ideas on repairing? Dab of silicone?