Hey all, having issues with my 2001 GS500 twin.
TLDR hanging idle, weak low-end. Possible lean condition? Still investigating.
Under load, she chokes and stumbles, power comes to the bike at just over 3K really starts to pull at 4k. She pulls all the way through to rev limit from there really smooth and predictably.

Full story and details.
Bought this from a dealer who couldn't get it running, has 10k miles and is showroom quality clean. I mean CLEAN. probably garage kept, no dirt or grime anywhere on the bike. she's beautiful.
Opened up the Carbs to take a look and saw a few issues, but zero dirt. Again, clean as a whistle. Dunked them in the ultrasonic just for good measure and re-assembled it. Here's where I started discovering signs of a very amateur job.

One of the vacuum slides was sticking, looked like the guy had a go at the slide needle seats with a sharpened screwdriver. The needle seat also was 'loose' and would drop out of its seat when I took the main jet and diffuser out. After a bit of fiddling I got the pair lined up and seated such that the vac slide moves smoothly and the seat is 'seated' for lack of a better word.
Looks like the guy had tried to balance the carbs without knowing about the sticking slide, as one of the butterflies was WAY out of whack, so I leveled them and set it up at 2.5 turns on the mixture screws, verified stock 17.5/60/127.5 jets. Everything was good to go.

She started right up! and up? and up?!? and UP!! Absolutely ran away, 4k idle.
after some investigating I found a high-flow HFA3503 in the airbox was not standard, so I got a OEM filter and fixed a folded airbox boot seat and tried again.

The results from those changes were better, but still had a bad 'floating' idle, where it would settle over 2 or 3 seconds and after warmup would stay at 3k for 4-6 seconds before coming down.

As it turns out, I have a non-stock exhaust! It's about 55mm wide at the junction, I understand stock is about 43mm (1 3/4" approx)
So I decided fine, we'll go jetted. I upped to a #130 main I had hanging around and put #20's in the idle jet and tested her out.
Again, above 3k she pulls good, steady, and hard. It's a ton of fun, as long as I never hit a stop sign.

So now I'm trying to figure out what I can do to smooth out the bottom end... She still has a slight hanging idle, and really hates pulling from idle.

Today I put in a #20 idle jet and #130 mains

So here's where we are now.

Mixture screw 2.5 turns
Jets #20/60/130
Needles +2 shims
Floats stock level
Filter OEM stock
Exhaust non-stock, about 1/4" larger OD after joint.

Behavior; smooth idle at 1100RPM
Smooth and powerful (for a GS) pull from 4k-top
Stumbles weakly from idle to 4k and has a 3-4 second delay returning to idle.

Note; I did a exhaustive vacuum leak check, had my assistant face away from the bike and signal if/when an idle change was noted as I sprayed brake cleaner around the carbs. None was detected. I can rule out a vacuum leak I think.
Note: New O-rings on mixture screws, new O-rings on main jets.

My thoughts on next steps?
no idea. I've got some #62 mids from another project I can drop in to play with. It seems like it's running lean but putting the mixture screws out to 4 turns made it bog down, didn't seem to help.
Unsure if i've got something I did not check yet.

For those who have well-running 2001 GS's, what's it behave like under 3k? maybe i'm just so used to the V-strom and KLR that I'm expecting too much of it under 3k?

ok
So, I think I know what I'm doing tomorrow morning.
Reading the CV CARB TUNING PROCEDURES on FactoryPro's website, [http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html] looks like I may have something.

The bike idles good but when 'blipped' will hang. So it's a lean right? Maybe
when at low RPM, it won't accept full throttle. My float heights may be too low, I may need to raise the float height to lower to fuel level to lean out WOT at low RPM's
The mixture screw can then be fiddled with.

I'm going to try that and report back in the morning.

You need to understand the fundamentals.

We are talking about the idle circuit, aka "pilot". The pilot jet supplies the fuel as air is drawn across it. There is a metered quantity of air coming over the pilot jet through a carefully sized little tiny opening in the edge of the carb throat. The bike should idle correctly with the throttle plates completely closed.

When you "adjust the idle", you are actually blocking open the throttle plates some fixed amount, which allows a LOT more air in than what is needed for idle, and that air does not go over the pilot jet, so it does not result in any additional fuel arriving into the mixture. This is why your idle is "lean".. It's not because you have not correctly set the pilot mixture needle ("air screw" ..SMH).

The reason it is delayed coming down from idle is that the slides go up when you open the throttles some, and that allows [more] fuel to come from the main jet (not the pilot jet!), because it's not running at idle anymore. It's running on the main jet. This is determined by where the AIR comes from. Since the throttle plates are blocked open some amount by setting the "idle speed", air continues to flow across the main jet and enough fuel comes in to keep the engine running at a higher than idle speed, which keeps the vacuum up, which keeps the slides up a little bit, which keeps the fuel coming in, and so on, until the pumping losses of the engine overcome the amount of available power and the engine slows and returns to "idle".

The problem with the idle is therefore twofold: 1. you have adjusted the idle speed too high, and 2. you have set the pilot mixture too rich.

Now, there is a reason you did this, and most likely that reason is at it's core one of two things (likely both). #1 on a 20 year old GS500, the o-rings on the pilot needles were most definitely hard and flat and probably formed into place, so once someone turned those pilot screws to try and adjust the idle mixture, it broke the 20-year-old seal and now fuel leaks past the o-ring making the adjustment totally ineffective. It will run super rich no matter what you do until you change those o-rings. And #2 you might also have clogged air passages in the pilot circuit, which require mechanical cleaning like by running a guitar string through them. Or ultrasonic cleaning of the stripped carb will fix it.

The stumble up to 4K you are getting is a symptom of the same problem, your pilot mixture is way too rich so it's very rich until there's enough air coming in to overcome all of the pilot jet's capacity and you are switching over to main jet.

If you look in my signature, there's a good guide on sorting this all out. Sounds like you have some other damage to the needle seat, emulsion tube, etc., so you might need to address that too. If it was me, and believe me I hate working on these carbs, but if it was my bike, I would bite the bullet and pull the carbs, do a complete and thorough cleaning and replace every single o-ring, plus the damaged parts you find along the way, and the float needles and seats. No motorcycle can sit with gas in the carbs for two decades without requiring major carb service. Mine can barely last a year.

You need 20/60/132.5 and 3 turns on air screw and 1 washer under needle. In fact your air screw being 2.5 is the likeliest culprit for your idle and just up issues.
Which country is this, US bikes have 130 mains from the factory. Unless you got some funky gas combination over there, you need 132.5. mains.
Cool.
Buddha.

Quote from: mr72 on June 18, 2022, 04:27:59 AM
The bike should idle correctly with the throttle plates completely closed.

Curious, not something I've ever come across. I'll put that in my 'things I didn't know" book lol.
I've read your step-by-step, I'm going to see if I can fix this by following your guide, I may just need to re-set the idle properly... but as of right now it will not idle without the throttle plates at least a hair open. Perhaps that's indicative of something.

A few notes.
1.) This carb is clean, sparkling, no varnish, no gunk. I did do a cleanout to include putting some weld wire in the tiny passages.
2.) All rubber has been replaced with the exception of the engine side boot O-rings, but as I had had no indication of a vacuum leak in that location using brake-cleaner, I suspect they're OK.


Let me get her warmed up properly and I'll fiddle with the mixture and I'll report back.

@Buddah, I'm currently running 20/60/130's, I'll get the bike warmed up and try that as well. A 2001 GS500 in the United States comes factory with... 127.5 mains? Could be wrong though, I've been wrong before.

I only use ethanol free fuel in my motorcycles
TO both of you, thank you so much for your attention and time. Let me work with what's been said for a day or so and I'll get back to you all.

US 01 bike I believe had 130 mains. I'm not sure, someone who has an 01/02 can confirm/refute. In any case 132.5 produces good results.
The throttle plates will have to be a hair open for it to idle, that's the function of the idle screw.
Cool.
Buddha.

Looks like I'll have to tear into the Carbs and inspect the through-passages better.

Got her warmed up after a 6 mile run out and back again, followed the 'how to set idle' in Mr72's signiture, seems he's probably right about how it had been set up.
Best I could figure it, after the bike was fully warmed up, idle at 1100rpm's she seemed to do best at 2 1/4 turns out. anything further than 2 1/2 and the GS would start surging under load under 2k, to the point where it became almost too weak to pull beyond 2k.

I've got 132.5's in the garage somewhere I'll pop those in, not that it should change my low end. Good shout though Buddah.
Thanks!

Not sure what my next step.
it's super close though, definately 80% more rideable than it was before I made these adjustments.
I'm gonna pop the 132.5's in while I think...

If you're holding perfect idle at 2 1/4 - your float may be too high.
Now check that with U tube method and if its not too high, you can run it - wont hurt anything.
Next - why are you riding it at 2K rpm, its completely useless below 3K.
Try 132.5, but you may be OK, just rev up, dont try 2k. In fact my bike is set to idle 1700 or so and 2K is where I am about to let the clutch out from a dead stop. The only reason for 2k to exist is that its between idle and 3k on a GS.
The tach used to start at 3K on the first gen GSXR's. These are 750's and 1100's.
Cool.
Buddha.

Yeah so I dropped the fuel level (raised the floats) by a hair, now the bike won't run...

-I'm gonna do a ground-up rebuild. I think that the needle seat that's kind of screwed up is giving me inconsistent fuel maybe idk.

Unfortunately I've been unable to find the vacuum slide needle seat on the market... anyone have any ideas?

-B

Quote from: BEVANS500 on June 23, 2022, 05:57:33 PM
Yeah so I dropped the fuel level (raised the floats) by a hair, now the bike won't run...

This is not cause and effect. The bike won't run because of something besides a slight change in float level.

Quote
-I'm gonna do a ground-up rebuild.

That's the right idea. Plus, you have to question the prior job that was done repairing the carbs. Does it have the right needles? Was an o-ring left out somewhere? was an o-ring left in when you did the ultrasonic? Are there leaks or pinholes in the diaphragms?

Quote
Unfortunately I've been unable to find the vacuum slide needle seat on the market... anyone have any ideas?

I'm not even sure what part you are talking about. Maybe find a parts diagram and point it out? The last carb kit I bought had a whole lot of parts that I didn't use, like emulsion tubes and weird brass needles. Maybe the part you need is included in a comprehensive kit.

Update y'all, been a while.

QuoteMaybe find a parts diagram and point it out?

The part in question was JET, NEEDLE (P-5M) 09494-00949, only found one dude in Great Britain who supplies them. Instead got a new carb brought in. The jet was super chewed up by a screwdriver or something by previous owner and wouldn't seat right, probably allowed a lot of fuel leak-by

New carb is in, runs a little lean, going to play around with mixture screws tonight.

go see the link in my signature to get an idea how to set the pilot mixture.

to adjust "the mixture", meaning like if it "runs lean" at anything except idle and low revs and 1/8 throttle, you have to "adjust" that by replacing jets.

I mean, how do you know it's running lean?

Hi All,
Got a similar problem to this hanging idle on a 2007 GS500F.
Bike runs well but it starts hard with choke fully on I have to watch it while is warms as I get the rest of my gear on.
I have to give it a little gas occasionally or it will die, idles at 1,200ish.
When I start driving it and pull up to stop signs or red lights the idle will rocket up to 4,000 and just sit there, choke is fully off.
If I release the clutch to that friction point the idle drops back to normal. Thought it was a valve timing issue so had a shop inspect the valves, they were good.
Same issue for the rest of the summer. Early September I decided to pop the carb out and do some cleaning and seal changes, I also bought a crappy Dynojet kit (yeah I know I shouldn't have now) and a drop in K&N. Planning on installing a Delkivic exhaust next year.
Cleaned the carb up nicely, was in decent condition except for the rust in the floats.
Dynojet only instructed me to change the pilot and main jets not the mid. Their direction was the main to be 128.5 but it was the 130 already.
They supplied a few different jet sizes in the kit so I went with the largest that was a 132 and the only pilot in the kit an 18 I think. Set the mixing screw to 3 turns as per directed.
Bike still starts hard and now idles erratically have to keep on the throttle or it will die. As I was warming it up I noticed the hanging idle disappeared at stops it would just want to die so I'd be revving it slightly even when warm. Also transitioning past 1/4 throttle the bike would seem to hesitate than rocket forward as the slide began to open. Started moving the mix screw out and nothing seemed to change with the idle still dies after 30 seconds running even when warm.
Figured it was running rich so I went the other way with the mix screw I have it around 2 1/4 now, the bike idles for 1-2 minutes then dies, if I flip the choke on the rpm jumps up then back to about 1,200 and the coming to a stop issue is happening again (clutch goes in rmp rockets up to 4,000 and sits there). If I let the clutch out slightly the rmp bogs down and if I am not quick enough bike stalls.
Most likely will buy new jets and do all 3 next year after the snow flies.
Any help with this issue I will be highly appreciative.
Also any info on companies that ship jets to Canada?

Do you have the stock needles sitting around ? Or you tossed them ? If you have them - this formula will work. If not, you're on your own.
You need 132.5 mains, 20 pilots and 1-2 washers under the needle, and 3 turns - and stay with the paper stock exhaust, dont switch to the drop in K&N.
And I make these into a kit and can send to Canadialand no problem. I'll save some $$ on the bolts cos they just add weight, and inside US it doesn't matter, but anything outside it could double your shipping cost.
The exhaust can swap is fine.

Cool.
Buddha.

Quote from: BEVANS500 on June 17, 2022, 08:29:51 PM
For those who have well-running 2001 GS's, what's it behave like under 3k? maybe i'm just so used to the V-strom and KLR that I'm expecting too much of it under 3k?

My 2002 with 89K mi is smooth under 3k...the carbs are the best GS500 Ive owned...much better than the pre 2001 E versions I had. The floats don't drift and it idles consistently, but mine is all stock. I love the engine of this bike for street use...no annoying flat spots just smooth tractable midrange.

I have a two bike line-up....newer bike, but will always have  GS500 in the garage as long as I can find another one.

Edit: now that I think about it not sure how much actual riding is done under 3k after take off, but I often creep in traffic etc. slow speed and don't have issues...dun remember exactly what rpm that is.

Just got back from a ride in DC Metro traffic....I do ride under 3k 2nd gear slow speed. Still idles stong...https://file.io/v4acNOg9XXlu

Yea an 01/02 carb rack is the best of both worlds. Have one waiting in the wings for when I find the time. I had it on my 95. But an issue in the petcock I misdiagnosed as carbs and put the older ones back in.
But really a 04+ carb is the same - just more complicated to take apart LOL.
Cool.
Buddha.

Quote from: adolling on October 21, 2022, 09:15:07 AM
Hi All,
Got a similar problem to this hanging idle on a 2007 GS500F.
Bike runs well but it starts hard with choke fully on I have to watch it while is warms as I get the rest of my gear on.
I have to give it a little gas occasionally or it will die, idles at 1,200ish.
When I start driving it and pull up to stop signs or red lights the idle will rocket up to 4,000 and just sit there, choke is fully off.

I have a similar answer.

Go read the post linked in my blog. Yes it's going to tell you to get rid of the K&N and put Mikuni jets back in. It'll also tell you how to sort out your issues.

Your idle is set too high, that's what's causing the "hanging idle". The reason you set the idle too high is probably because the jetting is wrong. Put a 20 pilot jet and you can sort out your idle situation. Put an OEM air filter in and you can probably sort out any running condition issues. And you will do well to prevent premature top end rebuild by putting a proper air filter in.