Idle mix unresponsive

[Dogma]

Hey gang, I'm just finishing up a carb cleaning and balance before deciding my 850 is ready to sell. Here's the thing: #3 is completely unresponsive to the idle mix screw. I can't kill the cylinder by running it all the way in, and backing it out 5 turns doesn't have any effect either. Idle is a bit rough, and it's a little rough under power at around 2000 rpm. Vacuum balance is even.

My theory is, a slightly PO-munged choke lever (Suzuki terminology for the little dingus on the rail that pulls the plunger out of the carb), is holding the choke circuit open just enough to mask whatever I'm doing to the idle mix. Any other ideas?

[Steve]

Have you verified the integrity of the mixture screw tip?

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[Dogma]

Nothing jumped out at me when I took it out to make sure the o-ring was there. I didn't examine it closely either. It didn't feel different from others when bottomed. I'll have a close look when I have time to get the tank off again.

I forgot to mention I left it set 2.5 out for the test ride.

[dantodd]

Have you pulled the plug wire you verify the cylinder is actually firing well enough too make a difference in the way the bike is idling?

[Dogma]

Have you pulled the plug wire you verify the cylinder is actually firing well enough too make a difference in the way the bike is idling?

I didn't think to try it. I guess because I was trying to kill the cylinder, rather than find out why it was dead. I'll add it to the list.

[Dogma]

OK, I finally had time to get back at this. Pulling the plug wire didn't change the way it was running (and made about 6 mm of arc). So, the reason I can't kill the cylinder by starving it is because it's already dead, and I'm too deaf to know the sound of a GS running on 3 cylinders. I tried running the screw from bottomed to waaay out (no spring tension) with no change. The point of the mix screw is in good shape, and the new lever on the choke rail has all of that working smoothly. So, it sounds like I need to go back and check the idle mix circuit like Steve showed me Saturday evening ('nother story).

Right?




For reference later, when I've forgotten: With mix screw and pilot jet removed, spray carb cleaner through the screw hole to verify clear passage into the throttle plate area. Cover the hole in the throttle plate area and spray again to verify clear passage back through the pilot jet seat. Use a couple drops of oil and compressed air for this one. Why not carb cleaner again?

[Nessism]

It's not unusual for a cylinder or two to not have a effect on the engines idle. As long as the bike is running well I don't worry about it.