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. :-k

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...

 

[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.

 

[Steve]

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.

That is only on the VM-series carbs, not the BS-series carbs that are in question.

The "choke" activation is completely different, nothing can be installed backward.

However, if the wrong parts might have been soaked (for any length of time), they could have been destroyed.

.

 

[DaveP]

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.

Intake boots and o-rings are in good shape. No rubber bits were dipped including the choke plungers. Airbox side looks ok, but I will need to get some spray and see if I can sens any further idle change due to a vacuum leak.

Nothing is sealing the airbox other than the two slide on clips that hold the lid to the box. Nothing else would be expected there per the parts diagram.

This morning, turned the pilot screws closed by a half turn, so now 2 turns open. Started fine and idles nicely for about 10 minutes before the idle started to ramp up.

Should also add that the tank is off the bike this whole time and running off of a portable tank with the golf tee stuck in the vacuum line.

Dave

 

[LAB3]

Nothing is sealing the airbox other than the two slide on clips that hold the lid to the box. Nothing else would be expected there per the parts diagram.


Dave

You probably wouldn't find that seal on the parts fische on mine either, it's glued to the underside of the lid where it mates up to the rest of the airbox. In my case, a bike that was garaged for 22 years before I bought it, there was a just a small remnant of foam left and a strip of goop where that foam had once been bonded on.

 

[DaveP]

I think I have things straightened out, but not sure if I can do anything to make sure the problem doesn't persist.

Removed the choke and throttle brackets from the carbs again and the engine was running perfectly. Idling at 1,400 RPM and would react appropriately to throttle input. Went ahead and completed the carb syncand thought I was ready to go.

Reinstalled the throttle cable bracket, still good.

Reinstalled the chock cable bracket, RPM's started to climb again. Pushed in the choke plungers manually (pushed the end of the rod that connects the 4 chock plungers) and idle settled back down. It is just fractions of an inch that I can play with the choke plungers to either have the engine run correctly or accelerate with a little bit of chock added.

It is a simple push pull system for the choke. Not sure how to make the plungers reseat better.

The chock cable is fairly new. It was provided by the PO uninstalled when I bought the bike.

Happy with how it is running right now, but consistency without input would be nice.

Dave

 

[1948man]

Did you make sure there is a tiny bit of slack in the choke cable before it starts to actuate?