Idle troubles

[mr72]

OK, I'll keep talking to myself here. Perhaps it helps some of you who follow along

I think I have been doing three things wrong:

1. expecting the bike to run right without any quirks even though it's 25 years old with 21K miles which may need valve adjustment and carb sync to be the best it can be
2. making adjustments before it was fully warmed up after a 15+ minute ride on the road
3. making too-coarse adjustments to the idle mixture... I was turning the screw 1/2 turn at a time

Oh and the other things I am doing wrong is being way too impatient and ignoring my instincts.

I read two other sites' posts that helped me a lot, maybe they are of use to you guys:
http://alt.motorcycle.sportbike.narkive.com/oHTaYnXK/blip-throttle-and-revs-hang-rich-lean
http://www.thegsresources.com/_forum/showthread.php?199096-Adjusting-the-Idle-Mixture-on-CV-Carbs

My gut tells me the bike is running rich at idle when fully warmed up. I can smell it, and it feels like other engines I have worked on that are rich. It may be totally ok for it to be running rich, especially considering it's summer and very hot and it'll lean out in winter, as long as I can keep it running at idle.

The hanging idle or slow return to idle I think was happening when the bike was not fully warmed up but off choke. I think I have been in too much of a hurry and assumed it was warmed up before it truly was. I just need to keep it on choke longer.

I really think it's running rich, but it's close. I can't ride this daily or even close. After I finish my MSF course this weekend I figure I'll be on pace to ride maybe once a week, very rarely a second time in a week. I just need to get it to where it will start when it's hot and it idles low enough that I can stop the bike without it revving itself. Then I can tweak it after my next real long ride while the engine is fully warmed up, and maybe lean out the idle mixture 1/4 turn max on each ride until it's right on.

Main thing is, if I can get it back to where it was on Saturday after I put it together, that is running fine but idling too low and you have to nurse the throttle a touch to keep it running, then that's probably good enough that I can work it 1/8 or 1/4 turn at a time every half hour of ride time until it gets more perfect or until later I can make time to adjust the valves and sync the carbs. It may never idle without bumping the throttle until I can adjust the valves and sync the carbs.

[mr72]

Update --

I rode it today until it was fully warmed up, then stopped a few times and set the idle speed. Once I got it home it was well warmed up (maybe 20 minute ride) and it was doing a little hanging idle. I wound up adjusting the mixture screws to a total of 3-1/4 turns out and there is minimal hanging idle and it will idle well as long as you are willing to occasionally bump the throttle.

Funny thing is, this is basically how it was running when I got it. But when I got it, it had a bad stumble and hesitation under 2K rpm and now it pulls great from idle on up. I never revved it over about 6K in the whole ride (all max 35mph streets neighborhood). I think the next step is to adjust the valves, which likely has never been done, and go from there.

Some things to take away:

- Adjusting the idle at anything but fully warmed up conditions is a fool's errand

- There are a ton of places for vacuum leaks to occur, ferret them all out before you try to tune the carbs

- Replace all o-rings in the carbs before you try tuning. Just like vacuum leaks add air where you don't want it, bad o-rings add fuel (and air) where you don't want it. That will ruin your tuning.

- Once you take stuff apart, don't put it back together until everything you can get to has been checked and fixed.

- 'Perfect' is probably too much to ask of a 25-year-old motorcycle with 21K miles, be willing to settle for "usable"

And finally, OWNING an old GS500 is a hobby in and of itself, separate from RIDING an old GS500

At the end of this little adventure I still have a bike that doesn't idle perfectly but it is at least usable. I'm not worried about it leaving me stranded or getting me into trouble.

[qcbaker]

Super psyched that you've made so much progress with this! Thanks for posting so many updates, I'm sure it will help people in the future if they ever have a similar problem.

Hopefully I can get my bike back on the road soon too lol.

[mr72]

For anyone who wants to follow a little more literary and less procedural description of this, check out http://joshkarnes.blogspot.com/2016/08/motorcycle-diary-pt-1.html

If you really dig reading some things I write, check out my books: http://joshkarnes.net/

That's all of the self-promotion I will do

[Arpee]

Pretty interesting thread, you write well enough to keep your audience engaged.

I had a similar problem with my old Katana 600 which runs 4 of these annoying carbs instead of 2.  As it turned out, after I'd done all the replacing of rubber parts (even the o-rings behind the rubber intakes) sealing every nook and cranny of the airbox, every o-ring in all 4 carbs (even the ones inside/under the needle jet holder...yep, there's one there too), turned out to be a poorly routed/adjusted throttle cable.  Unless you lay eyes on the butterflys with the throttle fully closed, it's hard to tell where a fully closed throttle is.  I ended up having to leave more play at the throttle tube than I like (in retrospect, I think the throttle tube should have been replaced) but just getting used to a different position of the right hand.

Anyway, on my GS I'm going methodically through the bike after I bought it from a PO who had a "friend" work on it for him.  The carbs were assembled all wrong with missing o-rings and flopping float seats--a wonder the thing ran at all.  Valve inspection and possible adjust is also being done after I remove all the over-tightend/seized bolts on the valve cover (actually have to drop the motor to get it done).  Bottom line:  never trust what a PO tells you, even if they are being sincere.  Most of the time, they have no idea what they're talking about.  The guy I bought my bike from for instance told me the carbs just need to be synchronized.  Well I knew it was much more than that and told him as much since I was going to start with rebuilding the carbs and adjusting the valves THEN looking at carb synchronization.

You're certainly right about the wrenching/riding ratio.  You gotta enjoy them both if you own an old GS.  Luckily, these old birds aren't too complicated.

Good luck finding the hanging idle.  What a pain!

[mr72]

Pretty interesting thread, you write well enough to keep your audience engaged.

Thanks!   Fortunately the readers of this forum are already interested in the topic.

turned out to be a poorly routed/adjusted throttle cable.

I have double, triple, etc. checked mine, and even put what the factory manual recommends, 5-10mm of free play. I set the throttle with a fair amount (over 10mm) of free play and then adjusted it at the grip using the barrel adjuster. I think I am in good shape here, but you never know.

Anyway, on my GS I'm going methodically through the bike after I bought it...  Bottom line:  never trust what a PO tells you, even if they are being sincere.

Right on!

Good luck finding the hanging idle.  What a pain!

Actually I think I fixed the hanging idle, but I'm left with an annoying idle condition where if you set the idle to the correct speed when the engine is warm, then part of the time, maybe even most of the time, it will try to stall at idle by idling too low. But if you increase the idle at all, I mean even 1/10 or less of a turn on the idle adjust knob, it idles at 2K+ rpm. I am actually beginning to think this is due to the 40 pilot jets, and that with the 37.5s that the bike came with from the factory it might be able to be tuned to idle a little better. For example, you cannot set my bike to idle at 1500 rpm. It just won't. It will either go 2K+ or just touch the knob lower and it's 1100-1200. My guess is that once you open the butterflies at all then it runs 2K rpms or more just because there's enough fuel at the pilot jet to run faster with the smallest amount of air you can get in past the throttles. With the throttles closed there is only enough air at the little bypass inlet whatever you call it to allow it to idle at under 1200 rpm. And due to some wear, poor state of tune, etc., mine won't idle consistently under 1200 rpm without trying to stall most of the time, so I have to constantly blip the throttle.

I just finished range day #1 of my MSF course and I have day #2 later today. I am doing the course on a Honda GROM. Now, first of all, talk about an easy bike to ride! And it's so unbelievably maneuverable. Anyway, I am rapidly getting hooked on how perfectly it runs (of course, these bikes are band new, less than 100 miles on them). Starts every time, idles absolutely perfectly all the time, can sit for 10 minutes straight at idle and just run without a hiccup, never hesitates or has to have the throttle bumped, etc. The GROMs are fuel injected while the other bikes (V-star 250s, an Eliminator and a DR200) all have carbs and they have that old school tendency to stall sometimes and you have to get the choke right and all that. I really like a lot of stuff about this GS but I'm telling you it's quite tempting to consider replacing it, promptly, with a fuel-injected Honda. And the tinkerer in me is working furiously on a plan to retrofit the CB500R's fuel injection to my GS

[mr72]

BTW, all... this is really good, if you can work around the occasional imprecise English:
http://members.ziggo.nl/minara/word%20bestanden%20website/Carburetor%20MIKUNI%20BST33.htm

And this looks like a winner!
http://stenhouseracing.com/shop/index.php?main_page=product_info&cPath=5_4&products_id=1

Kind of spendy, though. However, it sure would make adjusting those things way, way easier.

Learning that there are Aprilia, BMW, KTM and other Suzuki motorcycles (plus many more) bikes that share these Mikuni BST 33 carburetors really opens up the options on parts. Plus some of these owners are more technical or more likely tinkerers, and many have even replaced their carbs with NEW carbs, especially non-CV carbs. For those like me, who detest this carb design, this could be great. I mean, why spend so many hours rebuilding, tuning, etc. to get them close to right when you can flat out replace the entire carb with something brand new that will work perfectly from day one? And be easier to tune?

[Arpee]

many have even replaced their carbs with NEW carbs, especially non-CV carbs. For those like me, who detest this carb design, this could be great. I mean, why spend so many hours rebuilding, tuning, etc. to get them close to right when you can flat out replace the entire carb with something brand new that will work perfectly from day one? And be easier to tune?

Here, here.  The BST 33 wasn't too bad on its own on my DR350, but start lining them up in pairs and things get messy quick.  The CV carb gets good gas milage and offers smooth response which is great on the street.  That's about where the pro's end.  The con's are as long as the arm, starting with fiddly air leaks and goof-ball petcocks...it goes on from there.  Fuel injection is a welcome relief from all this.

[mr72]

Well, my problems persist.

Today I rode over to the gas station to fill it up (was on reserve to get there) and it died once at a stop sign, then wouldn't start again after filling it up. There's fuel all over the outside of the carbs and dripping onto the top of the crankcase from somewhere. My guess is it's flooding.

So, it's going to be back to the gas station with a trailer, bring it home and then tear the *@#$&$#%! carbs down AGAIN!!!

[mr72]

Out of frustration I bought a set of carbs from another forum member that I hope will be in better shape than the ones that came with this bike. Given the general condition, broken stuff, jury-rigged, holes filled that shouldn't be, epoxy on the carbs to fix (?) leaks, etc., I think these carbs may be a lost cause, best used for spare parts. The replacement pair is a cheap/quick fix.

However, in the long run, presuming a lot of factors like I can put a thousand miles on this bike over the next six months and I decide I am going to keep it for >1 year, I think I may spring for a pair of Mikuni VM32s and convert to something that requires less perfection to work. Considering I can buy VM32s brand new for $80-90 each, along with throttle cable and other misc. things I might need I think it may well be worth $200 to get brand new carbs on there that are not such a pain to tune.

[rabies]

Thanks for all the details. Following intently.

[mr72]

When it rains doesn't rain, it pours floods.

Well, I got the "new" carbs in, and they seem to be intact and in good shape, but for kicks I pulled the bowls and cleaned them, verified the float height and pulled the jets to verify the size (40/125). Gave it a cursory cleaning on the outside of the carbs, set the idle mixture screws to three turns out and mounted them on the bike.

Unfortunately I left it on prime and wound up with a cup or so of gasoline on the floor of the garage after leaving it sitting for a few hours. I suppose that answers the question of whether the float needles seat perfectly. Annnd... of course it wouldn't start. Which is wonderful.

I put the petcock back to Run and put it on the battery charger just in case, since I anticipate having to crank it it a lot to start it. But I am hopeful it will not only start, but it will idle correctly once I get a chance to try it this evening.

BTW I may have found the (another) cause of a lot of my problems with the old carbs, again quite by accident. See, when setting the float height on the "new" carbs, I noticed that the float needles don't constantly try to fall out. They are basically stuck in there, although I don't know exactly how firmly since I didn't try to remove them. On the old carbs, setting the float height is quite a challenge because the float needles fall out constantly when you tip the carb. Something tells me there must be some kind of o-ring or seal in the float needle valve holder that holds the float needle in place, and that part is missing or bad on my old carbs.

I seriously doubt that's the ONLY remaining problem on those old carbs, so they are best meant for the junk bin.

[MichaelM3]

Like @rabies I too am following intently. This has been an epic journey and I have nothing but admiration for your tenacity.

[mr72]

Thanks for that.

Unfortunately my tenacity is going to have to go up a notch. The bike won't run with the new carbs. This is what it does now:
https://www.youtube.com/watch?v=MA9jmxpkeCk

Frustrating to say the least. My current quasi plan, at least until a person more intelligent or experienced than I advises me otherwise (likely in the other thread I started about this) is to pull the "new" carbs off, take them all the way apart, double freakin' check everything, replace the jets with the new ones from the other carbs (that were working, so I know they are not clogged), run a .015" guitar string through the pilot orifices, and transfer all of the new o-rings I can from the old carbs to the new.

My present theory is that the "new" carbs have clogged pilot jets which is why it won't start/run. Or the fuel orifice feeding the pilot circuit is clogged. Or something I have no idea to check is bad.

In general these replacement carbs are in far better condition than the others and in theory should work better eventually. They reportedly came off of a motorcycle that was running, at least much better than mine is now. I put 6 oz of Berryman's B12 in the tank, and I bet if I could get the thing to run a little while it'd start to clean itself out.

[MichaelM3]

For the very little that it's worth, I agree with your theory. If the 'new' carbies have been sitting for a while with old fuel in them this could lead to clogged pilot jets.
Thinking 'happy thoughts' for you.

[SirHansford]

Disclaimer-  Just trying to help with some ideas but I'm a noob so some of my ideas might sounds silly to the old hats! haha.

Hiya man,  i'm still following your journey with this bike.  I'm no ace mechanic by any stretch of the imagination or even knowledgeable (i usually just know enough to get myself in trouble lol)  but I do like to tinker and do a lot of reading on subjects i'm interested in.   Thought i'd toss out a few ideas for you to maybe check over.   You say you think it's running rich and you run into most of your problems after the bike is warmed up?   Have you checked the fuel pressure regulator?  Ive read that they can cause hard starting and richness after the bike is warmed up when going bad .  And that might account for why you can never seem to get the mix adjustment screw dialed in proper without it going wonky quickly after.

Also,  you are thinking there might be a vacuum leak somewhere that you're having trouble nailing down,  maybe you could try the smoke method of testing? I've seen a big 1000 dollar smoke machine tester that is used in  shops,  but i've also read about just using a cheap 99 cent cigar,  puff away and blow it into an open line (or put a longer spare hose onto a point in the system to make it easier) and try to see where any smoke my be escaping.   I'm not even sure if this would work in this application as i've never done it but it might be worth trying and i'd be interested to know if it works.   Could also take a peek at the vacuum damper.  I'm not sure if those are prone to go bad or not but it's something to look at if you can't nail down the vacuum leak and you're sure there is an issue with vacuum.   Thanks for keeping us updated and I will continue to follow your thread till you prevail,  and i'm sure you will!  Good luck 72.

[mr72]

Disclaimer-  Just trying to help with some ideas but I'm a noob so some of my ideas might sounds silly to the old hats! haha.

Thanks for that. These ideas aren't silly but they may not all apply.

You say you think it's running rich and you run into most of your problems after the bike is warmed up?   

Well, with the previous carbs I think I got the mixture fully sorted out, but the bike still would not idle consistently. Unknown why. Got sick of trying to work on those carbs which had unfixable potential problems, so I decided to change them to a "new" set that have yet-undiscovered, but maybe fewer and more fixable problems.

Have you checked the fuel pressure regulator?

No fuel pressure regulator, or fuel pump even, on most carb'd motorcycles. Certainly not on this one.

Also,  you are thinking there might be a vacuum leak somewhere that you're having trouble nailing down,

That's not a bad suggestion if the "new" carbs seem to have a vacuum leak. The original carbs may have had vacuum or fuel leaks that I had not yet addressed, and I suspect maybe some that could not be repaired. If the "new" ones exhibit vacuum leak like symptoms (if I can ever get it to start!) then I'll try the smoke.

Thanks for keeping us updated and I will continue to follow your thread till you prevail,  and i'm sure you will!  Good luck 72.

Mostly I just write here because I have nobody else to talk to about this stuff. Perhaps some knowledgeable folks will continue to chime in and help sort this out, and then later on others who may have similar problems with their quarter century old bike will have some info that might help them identify their problems.

Speaking of which, here's today's update:

I went out this morning to pull the carbs back off and inspect and clean some more. First alarming thing I found was that the right carb had no fuel in the bowl. Opened the drain screw, nothing came out. Once I got the carbs off, I pulled the bowl, no fuel. Dry as a bone. Why? Oh, because the float needle valve was literally stuck in the seat. That was likely a big part of my problem.

Also I discovered another alarming issue, my own fault. On the other carb, the spring in the top of the diaphragm was misaligned and would have caused the slide to never open, if the bike would ever have run enough to generate enough vacuum to try and pull up the slides. Fixed that.

And I discovered a crack in the vacuum hose going to the petcock. This is double bad since it would create a vacuum leak AND result in cutting the fuel supply. Fixed that.

I swapped in the known-good (not clogged) 40/127.5 jets from the other carbs (bike has equivalent of a "slip-on" exhaust, so bigger mains make a little bit of sense). Had a heck of a time getting the old pilot jets out of the "new" carbs. I didn't check (yet) if they were clogged. I also swapped the float needle seats (with new o-rings!) from the original carbs into the new, and ran a guitar string through the orifices to make sure they were not terribly clogged. Then I put everything back together. I did this whole entire job in less than an hour and had the bike ready to attempt starting.

And... well it wouldn't start. But I think that's because I had the petcock on "Run" instead of "Pri" ... if I put it on prime it may start. We shall see.

Also the overflow fuel hose was still attached to these carbs when I got them and I am reusing it, but it was pre-bent into a shape that wants to run below the airbox and down by the rear shock. Now, I may not be a physicist but I do think that if it does ever overflow that it will siphon constantly since the overflow hose runs below the carb bowl. I guess it hardly matters since there are more serious concerns if fuel comes out.

After work today, I'll see if it'll start. I still have a lot of idle speed setting and etc. to do. But as usual I am optimistic and hopeful it will eventually work. But I am coming close to my tolerance limit for working on this bike. I think if it doesn't start and run mostly correctly so I can ride it after this latest escapade, I might trailer it to a shop and hand over my wallet... or alternately I might go ahead and bite on that $200 worth of brand new VM32s and at least eliminate wear and tear from my list of concerns. I hate to admit it, but this is so annoying that I'm contemplating getting it limp-running enough to sell it, try and get most of my money back, and buy a FUEL INJECTED ER-6n instead. I don't mind having a cheap motorcycle that I occasionally have to tinker with, but I am beginning to be sick of having a cheap motorcycle that never will run and I only ever get to tinker with. I think I'd get a lot more riding enjoyment from one of those little GROMs from the MSF class! At least they would start and run every single time!

[mr72]

OK quick update:

I just had a few minutes, went out to start it up having put the carbs back in a way that might work and it started up and ran like a scalded cat. Revved itself to about 7,000 rpm until I turned down the idle, something like 3K, to let it warm up. I think I turned it down too low. I only ran it a couple of minutes in the garage and then tried turning off the choke and it died and won't start back yet but these are problems I know how to fix.

The awesome news though is this: NO HANGING IDLE!!! That's a tremendous improvement over before. And it revs and runs like crazy. I think it's very close to 'right'.

I truly think I just need to get the idle speed and mixture set correctly with it fully warmed up and it'll be good to go.

"new" carbs + new jets from old carbs + new o-rings + thorough carb cleaning/declogging = RUNS!!! I do realize I'm basically back to square one but before there were no other squares to advance to while this time I think I might actually get past 'Go'. There is hope. I'm putting away the explosives.

[MichaelM3]

As they say at the football - "Played hard! Done good!" 

[Endopotential]

Hey Josh, just want to keep cheering you on!

Just finished my own GS project this summer, and took apart the carbs at least twice in the process.  But totally worth it, it's such a fun bike to ride.  With the tweaks I made, it runs about as well as my Yamaha R3 which is 10 years more modern.

A couple random suggestions:
- these bikes seem plagued by vacuum leaks.  I removed the PAIR system; capped off the white plastic discs at the top of the carbs; switched the stock petcock with a simple on/off mechanical lever.  Lots of threads on this forum about this process.  The bike runs great with these modifications.

- make sure the slides bounce up and down easily without the least resistance.  This was the cause of my hanging idle. I had oiled their surfaces in the mistaken belief that it would help the process, and only made things worse.  Bone dry or a light spray with WD40 did the trick

- the bracket /slide plate that opens and closes the choke on the carbs can bind.  I had to put in delrin washers on mine to get it aligned properly, so that it would slide easily back and forth.  Before this, I really wasn't off choke when I thought I was, due to binding

- run the bike with the gas tank and air filter off (run a temporary fuel system with a funnel or turkey baster, but stay safe).  This way you can check to see if the slides open and close correctly as you rev.  Also check that your throttle cables are behaving.

Best of luck, and rock on!