My GS started acting up today. It runs a little sluggish from 3000 to 4000 rpm, but then it's going *really* slow from 4000 to 5000 rpm. As soon as I get past 5 - 5.5 it runs great.
If I set the choke at 10-20%, the problem goes away, so I guess that means I'm running lean?

It's 1995 GS with stock air filter, but performance exhaust.
Carb has been cleaned.
Air mixture screws are set at 2½ turns out.
It starts and idles without problems.
I think the Pilot jets are #40 and mains are #125.

The clip for the needle is at it's highest like this:

So if it just started acting up, what did you do different?  We need more info!

If the jetting was good before it shouldn't be bad now unless you moved to the top of a mountain, so we can rule that out. 

Having said that, is that a picture of your needle? That looks like a dynojet needle in the third groove.  Are you saying you have the same needle in the first groove?  The first groove is pretty lean for a bike with a slipon and would give you the symptoms you describe...but wouldn't happen overnight.  

Quote from: ineedanap on April 07, 2010, 12:10:36 PM
Having said that, is that a picture of your needle? That looks like a dynojet needle in the third groove.  Are you saying you have the same needle in the first groove?  The first groove is pretty lean for a bike with a slipon and would give you the symptoms you describe...but wouldn't happen overnight.  

That's a picture of one of the needles just before I installed it in the carbs.
I thought the putting the clip in the first groove would raise the needle (making the mixture richer) ?? I'm pretty sure some one on this board told me that. I'll try to find the thread.
I changed the needle height during the winter when I cleaned the carbs.
EDIT: Here is the thread: http://gstwins.com/gsboard/index.php?topic=51178.0

Quote from: bombjack on April 07, 2010, 08:45:59 AM

Using the picture you posted, the first clip position from the top is #1.  In the photo the clip is on #3.

You said your clip is at its highest position.  If that means your clip is currently in #1, you didn't raise the needle, you lowered it.  Raising the clip lowers the needle, and lowering the clip raises the needle.  Sounds like you had the right idea but just moved the clip the wrong way.  If you went from #3 to #1 you leaned out the mixture substantially.  

The link agrees with me.    (see buddha's reply post #11)

Quote from: ineedanap on April 07, 2010, 02:57:58 PM

Quote from: bombjack on April 07, 2010, 08:45:59 AM

Using the picture you posted, the first clip position from the top is #1.  In the photo the clip is on #3.

You said your clip is at its highest position.  If that means your clip is currently in #1, you didn't raise the needle, you lowered it.  Raising the clip lowers the needle, and lowering the clip raises the needle.  Sounds like you had the right idea but just moved the clip the wrong way.  If you went from #3 to #1 you leaned out the mixture substantially.  

The link agrees with me.    (see buddha's reply post #11)

OK, seems like I did it right then   . The clip is currently in position #3 (just like in the photo).

How about the air mix screws? If I adjust them, will that do anything to the midrange rpm area?

Thanks for your help. I really appreciate it.

Mixture screws - Maybe.  Can't hurt to try.  

Other post - Cool, I kind of figured you had it right.  It sounded like you already knew what you were doing.  

Does it bog at a range of throttle positions, or just a specific throttle opening?  Throttle position gives you a pretty good idea of what carb circuit is not playing nice.  

Did it run good right before the miss started, or did you clean the carbs to try and fix a miss that was always there, but is now worse?

I cleaned the carbs and rejetted during winter. It ran quite well during early spring, but yesterday it started to bog at low and mid range rpm. I did'nt change anything right before this happend.

QuoteDoes it bog at a range of throttle positions, or just a specific throttle opening?

It bogs down the closer I get to mid throttle position. But it's also noticeable at 1/3 throttle, and then getting worse up untill 2/3 throttle.
I'm quite sure it's running lean somewhere, somehow, because it helps when I use the choke.

could be a partly plugged pilot jet?

If it ran good this spring and now overnight it doesn't, it's going to take some work.  I'm with intergalactic, something got plugged up somewhere.  If it was me I'd start from the beginning.  

Make sure you have fuel.  
Run the bike in prime to rule out the petcock.  
Open the gas cap to rule out a vacuum problem.  
Clean /replace the fuel filter if you have one, put one on if you don't.  
Clean the carb again.  
Spray down the intake boots with wd or carb cleaner to check for a leak.  
Rebalance the carb.

It sucks, but I don't really see any other options.  Hopefully somebody else has some better ideas.  

I guess as a last resort you could try moving the clip down to #4 on your needle.  Everything you describe points to a lean needle position...except for the part that it ran good the day before.  

So, I did a complete carb clean and adjustment again but it did'nt solve the bogging. 

I then checked the valve clearance and found that the right exhaust valve was really tight. It has less than 0.025mm clearance.

I'm going to adjust this valve soon, but can anyone tell me if a tight valve could cause this problem??

And if the bogging is caused by a tight valve, why does it help when I use the choke?? 

BUMP?

does it bog no matter the position of the petcock? (on/res/pri)
not 100% sure but it could be the petcock is faulty. i was working on a 92 that would bog and die at low rpms when in the ON position, but when i turned it to prime the rpms would dip but still be able to stay on. (more adjustments on the carbs were needed) but the point being that somehow there wasnt enough gas flowing at lower rpms, yet  sat high rpms was fine.
i'd say try switching to PRI and see if that affects the throttle response. and check float height cuz that really helped too.your floats may be sticking/needles wearing out

Quote from: pandymai on May 02, 2010, 11:02:52 AM
does it bog no matter the position of the petcock? (on/res/pri)

I just tried all three positions on the way home but it did'nt help.

Quote from: pandymai on May 02, 2010, 11:02:52 AM
not 100% sure but it could be the petcock is faulty. i was working on a 92 that would bog and die at low rpms when in the ON position, but when i turned it to prime the rpms would dip but still be able to stay on. (more adjustments on the carbs were needed) but the point being that somehow there wasnt enough gas flowing at lower rpms, yet  sat high rpms was fine.
i'd say try switching to PRI and see if that affects the throttle response. and check float height cuz that really helped too.your floats may be sticking/needles wearing out

My petcock is new so I doubt that's the problem. You could be right about needle wear. I will check that when I adjust the valves.
Thanks for your help 

I was having the SAME issue on my '00... (well, was having more than one, but seem to have gotten a handle on the hanging idle).  I pulled the carbs, bought a rebuild kit, cleaned everything, replaced fuel lines, removed inline filter for now, worked on mix screws 1/2 turn at a time, sync'd carbs, mixture screws some more, sync'd again, new air filter, checked slack on choke/throttle cables, reassembled... and ONE (if not the combo of all) of those things seemed to clear up my flat spot... helpful? probly not... but there is hope!

Thanks for all your replies! 
I did the valve adjustment and they are now all within spec, but that did'nt solve the problem.
I then cleaned the carbs for the umpteenth time and checking needle for wear. Seems just fine. I also put the c-clip back to stock position. Reassembled everything and went for a testride, but the problem was still there   
brentphx: I've done most of the things you mention except new air filter (looks fine though) and working on mix screws 1/2 turn at a time. I've ordered a new airfilter just because I'm getting desperate here. Will try doing the air mix screws too. I have them at 3 turns out now.
I might try some bigger main jets too.

The problem has gotten much worse now. The bike stutters, backfires and pops and refuse to rev beyond 3000 rpm.
I've checked the plugs. The right one is perfect but the left one is carbon fouled. I guess that means the left cylinder misfires.
I'm absolutely sure the carbs are not the cause. I've checked, cleaned and adjusted the carbs so many times now.

Any ideas??

Have you checked the plug for firing? Have you checked/replaced the leads?

Michael

Problem solved!! 
It was the wire from the left coil that had worked it self loose. At first this would give a few misfires at 4-5K rpm, but as the wire loosened the bike would run worse at low rpm's as well.
Thanks for your help 

Congrats on keeping with it and tracking it down!