Hanging idle; still confounded after research, LONG with a twist at the end.

[birdman]

Hello all.
I have recently acquired a very nice '99 GS.  Low miles very clean.  After riding it a couple times I had this to note.

The idle speed hangs up in the 4k range and the thing bogs badly off the line.  Also, between shifts the rpms hung also, very disconcerting.
I can't seem to get it to idle correctly.
I do what I know best.
First I searched the internet hi and lo and found this place.  I found a lot of other info, but most of the stuff I found related was here.
Next, after not seeing a clear path. Take it apart!

I removed the carbs and cleaned the fuel circuit thoroughly.  All orifices had buidup, some sediment in the bowls, float level was low.  All hard parts were in good condition and working order.  The small jet was truly junked up and the main looked pretty good. Idle jet and needle were a little crusty too.
I put it all back and ran the bike to where I could watch the inlets.
All is basically to factory spec and the idle mixture screws are at 3 turns.  (BTW, I am at 6000 ft above sea level)

After a good warmup I adjusted idle speed with the adjuster and ran the motor up and down.  A couple of times it still hung up.
As soon as I adjusted the idle screw it would drop quickly.
I did note that under WOT the fog in the left carb did not look as full as the right.  Might be a slight balance issue but nothing significant.

All buttoned up I took it for two separate rides to see the results.  Much better overall performance.  Less bog off the line and it sounds good all up through the rpm range.

But,  I come to a stop and the idle hangs at 3500.  I let a little on the clutch and it comes down.  Once stopped again with the same condition I adjusted the idle screw, yet again, and got it to sit at 1200 rpm.

I keep reading how this is a lean mixture acceleration affect. 
\Yet I can almost duplicate the same affect using the CHOKE. Mine seems to close and open properly and it seems independently operated.
I have yet to see anything about how the choke system on these carbs may be affecting idle.  This is not what I would consider a lean affect since it stays there a long time.  The rpm range that the engine is turning when hanging up should be drawing most of its fuel from the mains or it would starve.

What does anyone know about this funky choke setup? 
What's the likelihood that this enrichment circuit is malfunctioning somehow?  IE allowing additional fuel to enter an otherwise lean environment.
Its almost like a little closed loop gets started and the only things that seem to affect it are throttle stop or load, both of which change the airflow in the engine. 
Is there a way vacuum could be leaking inside the carb/choke circuit to cause it to enrich???

Thanks for your patience and replies.
richard

[coll0412]

First thoughts are as follows.

1. Is it possible the choke is stuck on. Make sure the plungers return back into the carb when the choke is turned off.

2. Vacuum leak, there could be a vacuum leak on the bike that cleaning the carbs did not fix. Check the two caps that cover the port on the top of the carbs. They come off the black plastic cap on the top of the carbs.  Second spray some WD-40 around the carb boots and see if the idle comes even higher. This would indicate a vacuum leak.

[birdman]

The choke rod seems to seat properly, but I don't know for sure that it isn't bottoming out in the right spot. IE crap stuck inside.

The black plastic caps are in place.  I did not notice any anomalies when I had it all apart.

I will try the WD 40 trick again.  Maybe its more subtle than I expect if its a small leak.

Anyone have the choke mechanism apart.  Is it servicable???

[beRto]

There are a couple of tiny o-rings in the top of the carbs. It is common to misplace them on a carb reassembly. If these were left out, the engine would run lean and might give the high idle you've encountered. Are you sure you didn't forget them?

[T1z3R]

i have exactly the same problem with two sets of carbs ive had on my '95 GS. one set has been stripped, cleaned and rebuilt with new o-rings all round but still exhibits the problem. i bought another set off ebay that were straight off a running bike allegedley which i fitted at the weekend and am still running now.

they exhibit the problem as well. each time the revs hang they can be brought down by letting out the clutch or by reducig the idle slightly.

im no expert with carbs etc but i can follow instructions enough to know that this is not right and its driving me nuts

[coll0412]

i have exactly the same problem with two sets of carbs ive had on my '95 GS. one set has been stripped, cleaned and rebuilt with new o-rings all round but still exhibits the problem. i bought another set off ebay that were straight off a running bike allegedley which i fitted at the weekend and am still running now.

they exhibit the problem as well. each time the revs hang they can be brought down by letting out the clutch or by reducig the idle slightly.

im no expert with carbs etc but i can follow instructions enough to know that this is not right and its driving me nuts

Switching carbs and the problem still exists=not the carbs

You have an intake leak, and its probably at the carb boots. The backside of the boot also has an o-ring that seals it against the head. Spray some wd-40 around these parts when the bike is running and see what happens.


As far birdmans problem, you need to check the vacuum caps attached to the black plastic cap on the top(the bike would not run without the diaphragm cover(black plastic cap))
Sounds like a vacuum leak.

Birdman what happens if you let the clutch out a little, does the RPM come back down??

[birdman]

Vacuum caps are intact.
WD-40 test, no engine speed changes. 
The bike is VERY clean, 5000 miles on it and always garaged. 
I added some Seafoam to the gas and plan to run it out ASAP. 
Start with some fresh gas and go from there.

It idles great it seems.  But if the engine is run up to 6k rpms or so, load or no load, it takes a good 4-5 seconds to idle back down.

Which also brings up that my TACH stalls out at about 6K rpm and as the engine increases in speed it then jumps up to 8K.
Not sure what that's about.

Thanks for the input.  I will keep chipping away at it.

r

[beRto]

You mentioned it's a '99, but I didn't see the mileage on the bike.

Maybe the motorcycle is telling you that it would like a valve clearance check and carburetor balancing. 

[birdman]

You just missed my post, 5000 miles on the bike. 
I have been thinking I should at least check the valve clearances at this point.

Another observation::
While observing the sliders during throttle activity on the bike, they fluttered rapidly as the throttle opened.  I expect this is from the rapid rise and fall of the vacuum the cylinder is creating as it is revving up.  Is this a normal thing or should they open smoothly?

[gsJack]

I had the same problem the first summer I got my 97 GS which has the same carbs as yours.  I solved it with hot idle speed adjustment, when I came to a stop and it raced at 3-4k rpm I would reach under the carbs while sitting on seat and turn the idle knob down very slowly till the idle speed dropped to normal.  Had to repeat a couple times and it was good for the summer.  I never touched those carbs, no rejet, caps still on idle mix adjustments and never had any further problems for 80k miles.

I parked the bike in Sept 03 when I got the 02 GS and it sat most of the time for 3 years unless I needed a backup occasionally.  My son started using it last year and was never happy with the carbs till he rejetted them, they probably got plugged up with all the sitting unused.  No issues with the new 3 circxuit carbs on my 02 which has about 57k miles on it now.  Best GS's ever built were the 01-02, had the new carbs and no body work.   

Just saw your newest post, good idea to check the valves but my 97 didn't require any shim changes till 40k miles, still had the original intake shims at 88k miles when JP changed out the engine.  One of the exhaust valves was down to min thich shim at 80k.

[gsJack]

No problems with that 97 GS at 6000 feet:

[birdman]

NEW twist.
so I am reading about the vacuum accuated petcock and wondering if the diaphragm might be leaking gas through affecting the idle.

Previously I just unclamped the tank side tubes and put them back on the way they were.

Well, lo and behold, the previous owner has not gotten the routing right.
Main feed goes where it should but the reserve line and the outlet line are reversed.  Reserve port is leading to the carbs.. HMMMMMMMM

Since I have it apart I opened up the petcock and the diaphragm looks excellent.  Busted knuckle looks less excellent.

Off to the store for some new gas line.

[beRto]

Sounds like you're making progress    Keep us posted!

[birdman]

Well as some have already experienced, no auto parts stores carry light duty fuel line.  Its all heavy wall stuff that makes it almost impossible to connect to the tank.  I ended up using the original main supply line and replace the reserve and output. The reserve was soft like it got a chemical attack of some sort so it had to go.

The petcock now works as designed, which is a good thing I suppose.   

The idle however is still a little balky.  Thought I had it tweeked this morning. Did well all the way to work, no hangups. 
But on the way home it kept hanging in the 3-4K range and I kept adjusting it little by little.  Once it calmed down at home I stopped fooling with it. 
It seems to be real sensitive to operating temp.  The hotter things got on the way home the more succeptible it was to hanging up.

[beRto]

Maybe a problem with your float heights? (Kerry has posted an easy way to check this)

You may still want to consider a valve clearance check; if these are off odd behaviours and irregularities often result.

[birdman]

When I cleaned the jets I also reset the float height to nominal per the spec.  They were set a little high, IE too much fuel in the bowl when I did the initial measurement.

[birdman]

Update, Have not gotten to the work yet but since riding a bit I have found the following.

If I set the idle just above 1000 rpm the hanging idle stops.
I set it when at full operating temp.  It took a few tries since its very touchy.
But have three days' worth of riding and it idles down fine at the lights and stuff.

Any setting higher and it does the hanging thing again.
Cold idle is a little low so you have to manage that with the choke/starting circuit.

I plan to do a little minor tweaking with the mixture screws now.  I think the setup is just a little touchy at the margin and that's why it has been a common problem.  Small adjustments can make a big influence from what I see.

r

[theUBS]

http://gstwins.com/gsboard/index.php?topic=41185.0

I sure hope I don't have to endure the frustrations that you're going through.  Being new to riding, it would be greatly appreciated if things would just work the way they're supposed to!

[birdman]

I am not really frustrated, just that it takes a little time to get things right.
The solution from what I understand is to just put in size 40 pilot jets.  If that works then fine.

To get optimum out of the factory setup though without all that work I think you have to walk a fine line between too much idle speed air and not enough fuel to compensate for it.

I find it fun though to learn how it all works.  I am used to computer control automotive systems and this is much more finesse than plug and play with a laptop.

Hell, when the govt has satellite control over all our cars and can control them from a dark room, we'll still be able to start and run our bikes like there is no big brother.

[theUBS]

I am not really frustrated, just that it takes a little time to get things right.

I find it fun though to learn how it all works.  I am used to computer control automotive systems and this is much more finesse than plug and play with a laptop.

Hell, when the govt has satellite control over all our cars and can control them from a dark room, we'll still be able to start and run our bikes like there is no big brother.

I guess if nothing else I'll find the whole experience to be more rewarding when it all works out.  I hope to avoid doing anything too major for right now though being as I'm a bit of a novice.  I did update/add to my other post after messing with the bike for a few minutes today.  Hopefully things are on the upswing and I'll be afforded the opportunity to thumb my nose at big brother sometime soon!