Cleaned Carbs - Can't Set Idle

[DaveP]

1981 GS650L

Over the winter I broke down the carbs, dipped each for a week, and then put back together to be ready for spring. Carbs back on the bike today and running ok, but I can't reduce the idle. It is running at 2,500-3,000 RPM no matter what I do with the idle adjuster screw. Nearly backed the adjuster all the way out it seems.

Pilot screws were all set at 2.5 turns when put back together.

Original air cleaner system.

Intake boot o-rings replaced previously.

Thoughts?

Thanks,
Dave

[Dogma]

Did you do a bench sync? If not, the #3 carb could be adjusted all the way closed, and the other carbs still fairly open.

Or maybe something else is holding the throttles slightly open? Throttle cable too tight?

[DaveP]

I did bench sync before installing and then connected the carbtune which showed pretty good balance. During the carbtune and balancing I had removed the throttle cable bracket from the carburetor since it was in the way, but no effect on the idle.

Dave

[Steve]

I broke down the carbs, dipped each for a week, ...

This is the part that scares me.

I know the VM carbs start to get soft if they are soaked for more than a day or so, I don't know about the BS carbs.

I also agree with the carb sync idea. Take the carbs off the bike. Hold them up to a light, look at the sliver of light under the edge of each butterfly. Adjust so they are all about the same.

Note that the carbs don't have to be open very far to maintain a decent idle speed. Be ready to hit the kill switch if you have them open a bit too far on your first starting attempt.

.

[Tom R]

I once ruined a Keihin carb letting it soak for a couple weeks - how’d they look when you took them out?

[DaveP]

Well that sucks. They looked ok to me, but that doesn't mean much...
DSC01366.jpg

[DaveP]

Maybe another symptom to think about. No adjustments made, started the bike again today. Fired up on the first crank and was running around 1,200 RPM. As the engine warms the idle increases. Maybe expect that a bit, but it just keeps going. Was up closer to 2,000 RPM after running for 5 minutes or so.

[Rob S.]

Maybe another symptom to think about. No adjustments made, started the bike again today. Fired up on the first crank and was running around 1,200 RPM. As the engine warms the idle increases. Maybe expect that a bit, but it just keeps going. Was up closer to 2,000 RPM after running for 5 minutes or so.

What about the choke? Where was it set throughout this event?

[2stroke]

This is just a guess but could the slide needle be to high.

[DaveP]

Choke was fully open to start, but could close it pretty quickly without affecting idle.

[1948man]

What did you soak them in? The older stuff used to be a lot more aggressive? Maybe your stuff is milder. Also, if it needs so little choke, is it possible some jetting (Pilot or air) is wrong resulting in a rich condition? Is there any way you could assemble the choke rail that would make it choke when the lever is in the "off" position? Just wondering.

[DaveP]

1 gallon pail of Berryman's Chem-Dip. The pail is probably 7 years old.

Don't think it would possible to make the choke work in the opposite direction. Slides out with the pull on the choke cable.

All jets are original. Did replace the needle valves and valve seats this time with OEM parts.

[Grimly]

This rings a bell - the lifter arms that pull up the enrichment plungers can be fitted upside down. It's a subtle difference but it affects running.

[Tom R]

Those carbs look fine compared to the one I ruined.... it was 20 years ago, but I remember it being very dark and chalky.
The enrichment plungers should be fully seated and have a bit of play before it pulls them open. It’s hard to tell from you picture.

[LAB3]

OK, so it's running fine now but the idle creeps up after it gets warm, that's a pretty good sign of a vacuum leak. If you've replaced the o-rings between the carb boots and the cylinder head and those boots are supple and not cracked, the next place to expect finding one is where the intake side of the carbs mates up to the airbox. On my bike it takes just a little extra effort to get those right. The sleeves that fit over the throat of the carbs need a bit of attention to make sure they're well seated onto the carbs, I coax them into position by grabbing the lip of them with a pair of needle nose and moving them onto the throat of the carbs for a good seal. Working from there back making sure the clamps are properly tightened is important and making sure the air cleaner cover has a good seal is also important. There was a strip of foam on mine that had degraded over time, some weatherstripping from the hardware store took care of that problem.