Idle troubles

[mr72]

Hey guys-

Just getting some ideas before I start pulling stuff apart.

I just bought my '92 GS500E on Saturday (day before yesterday). It has a running issue, so I want to get some advice.

To start it, you have to open the throttle. PO was using the throttle cable barrel adjuster to set the static throttle position open a little bit. Choke it and start it cold with the throttle wedged open a little bit with the barrel adjuster and it'll start and run fine.

Once it's warmed up, of course, even if you take it off choke, if you leave the throttle adjustment like this then it idles at 3-5K rpm. So the routine the PO was doing was to start and warm up the bike on the stand with the barrel adjuster opening the throttle a little, then once underway set the barrel back down flush and then when stopping the bike, bump the throttle to keep it from stalling.

PO had done a lot of work on the bike to get it mostly sorted out including rejetting and a bunch of other issues. But this was the remaining issue and he said he didn't bother getting it dialed in because he could make it work just fine by not letting it really drop to idle. In other words, you can keep it from stalling by blipping the throttle a little bit when it's idling.

OK.

So my thoughts on this are:

1. maybe when the PO did the jets, he lost one or both of the "tiny o-rings" and one or both are missing.
2. maybe the pilot jet is just way out of adjustment and there needs to be a lot more enrichment to start without doing the barrel-adjuster trick
3. maybe there's a vacuum leak somewhere (in addition to or instead of the tiny o-rings) ... PO suggested "airbox boots" whatever that is
4. maybe (probably) the idle is just set too low and if it were set higher it would not try to die at idle

It's been pouring rain constantly here in Austin so I haven't done any troubleshooting. Mostly I want to know what to look for when I get out there with wrenches in hand, if I get a few hours break from the rain while I actually have time to look at it.

Regarding the idle being too low, the PO says that it can't be set so that it will idle high enough to not stall. What does this tell you? What could this mean?

I did verify that the choke cable is connected and pulling correctly. Also if it matters, I did get the impression that the PO is being pretty honest abut everything and also is a reasonably capable mechanic. IOW, I have no reason to believe that he either screwed something up badly or he's trying to hide something. I'm assuming there's some honest mistake (like losing a tiny o-ring) or one more thing to fix (other vacuum leak etc.). I just don't want to spend a ton of time trying to chase this down. Besides this the bike is 100% sorted and ready to ride.

My current theory/plan is:

1. need to adjust the pilot jets (choke) so that it will start cold on choke without having to block the throttle open
2. probably there is a vacuum leak somewhere preventing it from idling without stalling ... find and fix ... and here's where I really need help on where to look
3. once I get #1 and #2 fixed or verified, if it still misbehaves, could this be valve adjustment? I'm not sure.

Ideas?

BTW when the PO changed the jets, he said he went "up one size" on the main jet. I have the exact info at home but not with me right now to verify. If it matters, the bike also has a stainless Yoshimura muffler from a GSX-R750 on it. I suspect the main jet is not related to the problem.

Thanks and sorry for the long post, my second post!

[mr72]

Welp, not much response yesterday...

I'm going to pull the tops off of the carbs and ensure the "little o-ring" is not missing. My research seems to indicate the running issue I have is most likely caused by these o-rings being MIA. Might as well double check, seems pretty easy to get to.

I'm talking the suzuki part number 13509-17C00 o-rings, "#10" in the service manual diagram, "vacuum port" o-ring, this one:



If my google-fu is any good, then this is a 3.0mm x 1.5mm o-ring (3.0mm ID, 6mm OD, 1.5mm CS). Finding a metric o-ring locally might be tricky. Anyone know if a standard #006 o-ring will work? That's 2.9mm ID and 1.78mm CS for a 6.46mm OD. If so then I can probably get those at a local hardware store, even Home Depot might have one.

[qcbaker]

You seem pretty knowledgeable so this might be a moot point, and I see that you said the PO said the idle cant be adjusted high enough that it doesn't die at idle, but did you try to adjust the idle screw yourself? I would at the very least try that, just on the off chance that the PO was wrong.

[mr72]

haha I only seem knowledgeable because I read a ton here on gstwins.com ...

EDIT

Alright, I pulled the tops off of the carbs and those "little o-rings" were in fact missing. But someone had tried to plug up the vacuum port on the top of the carb with goop of some kind. That was unexpected.

BTW a #006 o-ring from O'Reilly Auto Parts fits perfectly. $1.29 each and there's an O'Reilly on every corner it seems.

I did eventually get it to idle when it was warm but it still wants to stall. Also had a heck of a time starting it with the choke on. I am guessing maybe the idle mixture? But now it has the o-rings so at least that's done.

[mr72]

Well well, the intranets win again!

I managed to figure out who the PO of this bike is here on gstwins! A little bit of easy searching and I read his posts which detailed the mod/repair history of the bike. It's a gold mine of information.

Anyhoo, I realized that the PO did the "vacuum petcock delete" like this: http://gstwins.com/gsboard/index.php?topic=58895.0  However, I wasn't told about this so my starting troubles were probably due to flooding ... I didn't close the manual petcock when I parked the bike on Saturday. Or last night for that matter.

And ... I also discovered that the PO didn't change the pilot jets, but did drill the pilot mix screw covers and according to his posts, "backed them out to 2.5 turns" ... which also explains hard starting, difficult idling, etc., and maybe also the bogging at 1.5-2k rpm.

So I have some more work to do. For now, adjust the pilot mix screws and adjust the idle, try to improve idle quality as much as I can an get the bike to idle consistently without stalling or throttle blipping if possible. Longer term, get some 40 jets and swap them, along with a thorough carb cleaning and inspection for vacuum leaks after reassembly.

One question: where do I get new pilot jets? I have read that they should be like $3 each but Jets R Us has them for about $5.79-7.50 each. Is that the right place to get them and/or a decent price? I think this bike is literally going to nickel and dime me to death. Is this something I might be able to get locally (Austin TX) in order to avoid paying $10 for shipping?

Thanks!!

Learning a ton here. this forum is a great resource.

[mr72]

I guess I'm [almost] the only one talking in my thread. But maybe I'll eventually say something that causes someone who knows an answer to chime in.

Yesterday I tried adjusting the pilot mixture screws, first by putting them all the way in and then backing out four turns. The bike ran fine but really did not want to start or idle without throttle, even on choke. At first I thought it might still be lean. I rode it until it was fully warmed and then tried to adjust the pilot screws again and couldn't get it to change idle speeds via the screws. Then I pulled the plugs and they were super black. It's running rich at idle, clearly.

After I shut the bike off I began to go through the pile of removed parts from the bike that the PO gave me, which included the original pilot jets. I guess the PO did change the pilot jets.

I cleaned the plugs and put them back, then reset the pilot mix screws to 2.5 turns out. The bike would not start back up, choke or not, with or without throttle. The engine was still warm, it had only been sitting maybe 15 minutes since riding.

So, now I've fixed the vacuum leak, verified the choke works, set the idle so it'll idle when warm, but the pilot mix was way too rich which is likely what was causing it to want to idle at 3K rpm to begin with. I've never gotten it to start without a lot of throttle AND choke, and it won't start now. I'm kind of stumped. Next up I think I need to just let it cool and try to start it again, but I ordered new pilot jets so maybe I should just wait until they arrive and bite the bullet, pull the carbs and thoroughly clean them and ensure the correct pilot jets are installed. Get it back to a known good setting and with known clean carbs and fresh jets. The jets will probably arrive by Saturday.

Question: if the PO happened to install 40 pilot jets, then what is the initial pilot mixture setting that will enable it to start so I can tune the pilot mixture?

Oh, and I despise those pilot screws. Really needs a knurled knob or a T-handle. Getting a screwdriver bit on that is a gigantic pain.

[Lbx!]

I have absolutely no helpful information to add to your post. I just wanted you to know you are not being ignored! I am reading because I am fairly sure I am going to have to do similar things to my GS once my parts arrive. Thank you for the detailed questions/answers. 
On a related note, yes getting a screwdriver in to those screws is a *insert profanity here*.

[grader]

stock pilot jet is a 17.5 so if there is a 40 in the bike now then that is the problem. they go up in 2.5 increments so a 20 or 22.5 would work as these bikes are lean from the factory.

[mr72]

stock pilot jet is a 17.5 so if there is a 40 in the bike now then that is the problem.

This is a '92. I think the stock pilot is 37.5.

I also think it has the stock main jets in it now, but there is a set of 127.5 in the parts bucket, and according to the PO's messages on the forum here, it sounds like he tried the 127.5s and went back to the stock. Or it's possible there are 125s in it now. Hardly matters, because the bike runs great at >1/4 throttle. All of my current running issues are at idle, light throttle, and low-speed (<2k rpm).

[mr72]

I have absolutely no helpful information to add to your post. I just wanted you to know you are not being ignored! I am reading because I am fairly sure I am going to have to do similar things to my GS once my parts arrive. Thank you for the detailed questions/answers. 

Hope this is helpful then. Since it's likely to rain all weekend this weekend, I think I'll plan to tear everything down and clean the carbs, change the pilot jets (assuming I get new ones by Sat AM), and I have some other stuff to do (change the ignition switch, handlebar and fuel cap, replace the tank bolts with correct bolt and maybe retap one hole, etc.). Might as well just tear it all the way down, then I can set the initial pilot needle position with the carbs upside-down on the bench where I can see the screw heads and easily count turns.

I assume 2.5 turns out is still the correct initial position.

The instructions for setting the pilot jet screw position generally are like this:

1. start and warm up the bike
2. set the idle at 1500+
3. turn the pilot screw out until revs stop increasing and then turn out another 1/4 turn
4. repeat 2-3 on the next carb
5. set the idle back to 1200ish

Now, my problem is that turning the pilot needle screw out does not increase revs. So I assume I can go backwards here, right? Set the idle at like 1500-2k, then turn the pilot screw IN until revs begin to DECREASE, then repeat with the next carb. Now do steps 2-4 on both carbs again.

My current theory is that the PO left out the "little" o-rings causing a vacuum leak at idle, resulting in a really lean mixture at idle. So he probably set the pilot needle really rich to compensate, which resulted in making it barely run at idle (closed throttle) but once the throttle opened the extra air from the vacuum leak was insignificant so it ran super rich while in the pilot circuit. This is why I had bad running (hesitation/bogging) at 1.5-2K rpms and also why the bike could not be set where it would idle below about 3000 rpm. Opening the throttle enough to get air in the throat of the carb resulted in a 3k rpm idle due to the super rich pilot jet setting, and backing out the idle enough to reduce below 3K rpm closed the throttle enough to make it run super lean due to the vacuum leak.

I fixed the vacuum leak and then the bike could idle but it was really, really rich, which is why it wouldn't start on choke and would die when I put it on choke even when cold. And it stalled at idle when warmed up. I initially (without checking the plugs) thought it might still be lean at idle and made matters worse by adjusting the pilot jet more rich. By the time I got half a clue what was going on, the bike was already hot and would not start because it was likely flooded or who knows what.

I'm going to steel myself to "do it right the first time" and go ahead and tear everything down, clean, rejet, and put it all back together by the book. That way I can verify everything is done right, or at least I can stop blaming the PO for what might be done wrong.

You guys can follow along and see what I find. I am sure a lot of these 25 year old bikes are in a similar state.

[SirHansford]

I'm not a huge wrench turner and am also a new GS owner,  so i'm learning a lot reading your thread.  Thanks for keeping us up to date on how your troubleshooting is going.  I'm sure i'll use this information in the future. good luck!

[mr72]

I'm not a huge wrench turner and am also a new GS owner,  so i'm learning a lot reading your thread.  Thanks for keeping us up to date on how your troubleshooting is going.  I'm sure i'll use this information in the future. good luck!

Yeah I think the real key is that when the PO rejetted the carbs he left out the little o-rings and then that started a crazy wild goose chase to try and get it to run right, resulting in nearly everything being set wrong.

[mr72]

For those who have been following along, here's the current state.

I tore down the carbs over the weekend to check what was up. I found a lot of things along the way. Lesson here is: you never know what the previous owners might have done right or wrong to the bike, so best to make sure and do the work right yourself. Or at least make sure compromises you make are those you have chosen for yourself, so you won't go nuts trying to debug something with no information on what might have been done wrong.

First thing I found was the vacuum hose going to the petcock was not in fact a vacuum hose. It was a fuel hose, and it was making a poor seal on the carb. So this is likely another source of a vacuum leak.

Next I found that neither the airbox boot clamps nor the carb boot clamps were tight (!). No wonder the thing wasn't working right.

Went to drain the carbs, one of them was missing the drain screw and the hole it goes in was filled in with goop... looks like epoxy. Brilliant.

Carbs torn down on the bench, the pilot jets had already been replaced with 40s. I put them right back. The main jets were the originals (122.5). The PO gave me a little envelope labeled "GS500 Jets" that had the original pilot jets and a set of 127.5 main jets in it... my guess is he originally got 40/127.5 set to use, could not make it run right with the 127.5s installed due to his numerous vacuum leaks, and put the 122.5s back in. I swapped them to the 127.5s.

There was some buildup of some white and tan crusty junk all over the bowl seal surface on both sides. I let the bowls soak in Dawn+water for about 24 hours then cleaned up with the Dremel with a nylon brush bit. The float o-rings were cracked and hardened and would not hold the floats in place, and the o-rings I had here were too fat and I couldn't get them to fit back together with the new ones. I have to order more o-rings but for the time being I made a game-time decision to put it back together with permatex just so it will run. Yes, I know I will have to tear them down again!

Float height was not even close to right, far as I could tell. Probably off by 3-5mm (high). No wonder it was flooding.

Everything was clean and good to go so I buttoned it back up. I didn't take the tops off since I had just done that the other day, and I knew the o-rings were good and everything was good to go. Dunno if there are shims/washers on the needles. We'll see how it runs. Easy enough to get to that part if I need to check or change it.

I set the pilot screws to out one turn, since there are 40 pilot jets and it was running poorly with them out 2.5 turns before.

Getting it back together was a colossal PITA. That freakin' airbox! I'm ordering a pair of pods right away! But one thing I DID discover is that to get the airbox back on, it REALLY helps to take the air filter OUT, and then push the airbox flanges onto the carbs from the inside of the airbox by reaching in the air filter hole. This literally took me over an hour to get the airbox on. I wound up actually pulling the carbs back off and putting the airbox on the carbs first then cramming it all back on together, which was easier, but not close to easy.

I added a blob of permatex on each of the broken-off carb top vacuum ports just for good measure, I don't want it to leak. Gotta order some new carb tops, or even find some used/broken or maybe a pair of carbs that are in bad shape so I can use them for parts, including these tops. And a new bowl for the one with the missing drain screw.

The PO had added an inline fuel filter and I debated heavily whether to chunk it. If I had any extra fuel hose on hand I would have just tossed it, but I didn't, so I didn't. But, I found that the fuel filter was really what was causing all of this to be so hard to assemble. There's just not room under there for a fuel filter along with everything else. With a lunchbox or pods it would be fine. If I wind up having to pull it all apart again, I'm putting new carb tops on, pod filters, and probably redoiing all of the fuel hoses and maybe change the type of fuel filter as well. I'll be shocked if that fuel filter is not pressing on a fuel hose causing it to be restricted while it's running. But there's no space to even get a light in and look so who knows? We'll find out when it runs.

Took surprisingly long to get the carbs primed but once it was all back together and I cranked it about 50 times it started right up. On choke! Which it wouldn't do before! I had to bump the throttle a little to get it to start but nothing like before. I started fiddling with the idle adjustment almost immediately and found that once it had been running like 30 seconds I took it off choke and it was idling at 5K rpm. I backed it off and got the idle close to right... I just had a few minutes to fool with it. But then I turned it off and the ultimate test. 5 minutes later I tried to restart and what do you know? It fired right up! Great news. Now at least I can ride it to the gas station, get gas, and not have to get a truck to take me home.

I still need to reset the pilot needles but at one turn out at least it was running far better than before.

Here's a question for the experts: what does it mean when it is slow to return to idle? I rev it and it comes down to like 3.5K rpm and then slowly (3-5 seconds) returns to idle. I am guessing it's coming off the main circuit and going to the pilot circuit and it is telling me it's still rich on pilot ... ? Also it seems to idle faster OFF choke, even when cold, so that's probably telling me the pilot is still rich. Am I on the right track here?

One thing's for sure, I know my way around the carbs a lot better and feel pretty comfortable working on it now. Well worth it. I think just a few minutes adjusting the idle and pilot mixture and I'll be in business. Eventually I'll have to pull it all apart again and put in new float o-rings but I'll probably wait until I can get new carb tops and a replacement carb bowl before I do that, that is assuming I can get it to run acceptably. The goal here is not to make the bike awesome. It's to make it reliable and usable to ride 100 miles a month over the next few months. This is Texas and we expect a far milder than normal winter, meaning it'll be highs in the 70s and lows in the 50s even in January. That sounds like perfect motorbike weather to me.

I'll update whether I can get the pilot screws and idle set right after I have a few more minutes to play with it.

Have fun and keep the revs up.

[Torstein]

I've been following along with this post, have had nothing helpful to say. But I'm cheering for you! Glad to hear you had some success over the weekend!

[qcbaker]

...

Here's a question for the experts: what does it mean when it is slow to return to idle? I rev it and it comes down to like 3.5K rpm and then slowly (3-5 seconds) returns to idle. I am guessing it's coming off the main circuit and going to the pilot circuit and it is telling me it's still rich on pilot ... ? Also it seems to idle faster OFF choke, even when cold, so that's probably telling me the pilot is still rich. Am I on the right track here?

...

Slow return to idle is a lean condition as far as I know. The way the choke works (if I remember correctly, could have this backwards, so maybe double check what I'm saying lol) is that "opening" the choke, is actually restricting airflow, if effect creating a richer condition (so really, youre "closing" the choke, rather than opening it). Then, as the engine warms up, you can take the choke "off", returning the fuel/air mix back to normal, which is normally a leaner condition..

Idling faster off choke and being slow returning to idle sounds to me like your fuel-air mixture is too lean. Try adjusting that, after making sure my memory isn't mixing up the way the choke works haha.

ETA:

Quick googling: seems to me that my memory is correct, but I did find this on Yahoo Answers: "Modern carburetors typically provide a rich start mixture by means of an orifice which supplies extra fuel. The orifice is normally covered by a piston which is moved by operation of the "choke" lever." Not sure if this is the case on the GS500, but its essentially the same thing: in a normal functioning engine, the further the choke lever is "open", the richer the fuel/air mix is. So, if youre getting higher RPMs with choke off at idle, and it is slow to return to idle, I would bet your f/a mix is too lean.

Found this thread too, seems to confirm the above http://gstwins.com/gsboard/index.php?topic=21206.0

[mr72]

Slow return to idle is a lean condition as far as I know.

And the internet confirms your assessment.

Actually I'll be quite pleased if it's lean, because before I tore it all down it was running so rich at idle that it would die and refuse to start up again when it was hot... it would really only run close to right when it was stone cold.

is that "opening" the choke, is actually restricting airflow, if effect creating a richer condition...
...but I did find this on Yahoo Answers: "Modern carburetors typically provide a rich start mixture by means of an orifice which supplies extra fuel.

Yeah I think the GS carb actually adds fuel when on choke as opposed to the traditional choke that closes the air inlet by some degree (to see in real easy action look at a weed eater ). No matter. I can adjust the mixture at idle. I only have the pilot needle backed out one turn right now, so lean running would not be surprising and it's easily fixed.

By the way today I bought one of these http://www.harborfreight.com/8-piece-right-angle-screwdriver-92630.html to adjust the idle mixture.


Idea is to use the "handle" to hold the bit in place and turn the knurled knob on the back of the tool to make adjustments. With the ratchet it's 20 clicks for one turn, so you can set it 1/4 turn by 5 clicks etc. Let's see if it works. Could make my life a whole lot easier. Man that screw is a huge pain to get to with ordinary tools.

I have everything I need to put it all back together now this afternoon. Kind of excited about it actually.

[qcbaker]

...

I have everything I need to put it all back together now this afternoon. Kind of excited about it actually.

Hopefully you get everything back in order. Happy to be of some kind of help lol.

[ShowBizWolf]

I'm in the same boat as Torstein... been following along but haven't had anything helpful to add... except good luck!!!

And also, thank you for sharing your experience... it may very well help others in the future 

[mr72]

Okay guys, here's the way it is.

I put it all back together and it started right up, no sweat. I had the pilot mix screws turned 1 turn out. Once the bike began to warm up, I took it off choke and the idle was like 4000 rpm. I adjusted it down and set to try to set the mixture screws.

Recapping ... I just pulled the carbs and cleaned and put them back together with 40 pilot and 127.5 main jets. Bike would not start when hot before and would not idle when warmed up. Previously it had 122.5 mains with the 40 pilot jets. It also had numerous opportunities for vacuum leaks.

Here's the current behavior:

- when I first started it, while it was warming up, it would be delayed idling down. Rev it to >7K and on the way back down it would hang at 3-4K for like 5 seconds and then return to ordinary idle. This was with the pilot mix screws set to one turn out. Right now, this is looking like a good place to go back to.

- I went about setting the idle mix screws once warmed up and by the book, that is 1/4 turn past where the idle stops increasing, they are each set about 3 turns out.

- when warmed up (or cold, actually), rev it on the stand and it will NOT idle down. It stays at 4-5K rpm. If I briefly turn on the choke it will return to idle and when I turn the choke back off, it will stay at idle. So it will idle off-choke, but only after I "blip" the choke on and off.

- the right carb idle mix screw seems to have no effect(!) ... could be that I backed it out so much that it now is as rich as it'll get and backing out more makes no difference

I know everyone said that delayed idling down indicates lean. Now I think I have it way rich. When we say hanging idle means lean, are we talking about a full turn on the mix screw or 1/4 turn or less?

[qcbaker]

...

- when warmed up (or cold, actually), rev it on the stand and it will NOT idle down. It stays at 4-5K rpm. If I briefly turn on the choke it will return to idle and when I turn the choke back off, it will stay at idle. So it will idle off-choke, but only after I "blip" the choke on and off.

...

I know everyone said that delayed idling down indicates lean. Now I think I have it way rich. When we say hanging idle means lean, are we talking about a full turn on the mix screw or 1/4 turn or less?

Based on our discussion about chokes earlier, "blipping" the choke on would make the mixture richer for a second. If that causes the bike to return to idle properly, then to me that still indicates that the bike is running lean, not rich.

Are you absolutely sure you've eliminated the possibility of a vacuum leak somewhere?