Idle troubles

[mr72]

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.

On the contrary, if I leave the choke on, that is I don't "blip" it, then the bike will die. I think it's just not returning to the pilot circuit AT ALL until I turn on the choke, which makes it run so rich it wants to die, and this causes the revs to go down and if I turn the choke back off when it gets to idle then it'll continue to idle.

It really feels like the bike just only is running in the main circuit and you have to force it to go to pilot by getting it to stall.

Come to think of it, a gross vacuum leak could cause this... that is air getting in other than the throttle plate.

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

Nope! But it's not exactly easy to check. How long will it run with the tank off? I think the tank has to be off in order for me to really check for vacuum leaks. I suspect the repaired hole where the balance vacuum ports used to be in the carb covers might be leaking still. And there are a hundred other places it could be leaking but to get any carb cleaner sprayed on there requires the tank to be off.

ALSO I just remembered, there was a drop of fuel on my screwdriver bit when adjusting the pilot mix screws. Is it possible a bad pilot needle o-ring could be causing this? Talking #17 in this picture:


If so, what's the spec/size of that o-ring?

[qcbaker]

I'm sorry, I don't think I'm knowledgeable enough about the carbs to be of much real help here... 

Everything from here on out is speculation on a subject I have limited knowledge of:

The only thing I can think of is that the pilot jet is very rich, but you also have a vacuum leak somewhere, causing the bike to run lean when on the main circuit and rich when on the pilot circuit? I'm not sure if that's even possible lol

[mr72]

I'm sorry, I don't think I'm knowledgeable enough about the carbs to be of much real help here... 

Well I'm not very knowledgeable about carbs and especially not this one but I am above average even among gearheads on this general topic... although I'd be far more comfortable working on the fuel map via a computer and megasquirt   I did do a ton of work with my 240Z carburetors long ago and they are similar enough to this that it's easy enough to translate.

Everything from here on out is speculation on a subject I have limited knowledge of:

The only thing I can think of is that the pilot jet is very rich, but you also have a vacuum leak somewhere, causing the bike to run lean when on the main circuit and rich when on the pilot circuit? I'm not sure if that's even possible lol

Yeah I think it's definitely NOT running lean in the main circuit. I haven't ridden it on the road since I got it back together with the 127.5 jets but I think with 127.5s and the stock airbox it's highly unlikely to run lean on the main jet.

But it MIGHT be lean on the pilot jet, but REAL lean at idle due to a vacuum leak.

My current (questionable) theory is that at small throttle opening (idle) there is air getting in one or more places where it shouldn't ... maybe the pilot needle o-ring or some other vacuum leak, and this causes it to run lean at idle no matter what I do. This entices me to adjust it way too rich. So when the throttle is closed it causes a big vacuum condition and sucks in a lot of extra air through the vacuum leaks and makes the revs hang, since the pilot is adjusted so rich that there's plenty of fuel to mix with the vacuum-leak air and keep the revs up even though the throttle is [mostly] closed. If I do something like choke it or even if I were to ride it and let it roll in gear and pull the brake, then once the revs get down low enough there's not enough vacuum to suck much air in and it returns to idle, but since it's leaking in air, it's very lean so it won't idle at a the correct speed and it tries to stall.

Basically I think the problem is likely continued vacuum leaks and possibly bad (or missing!) o-rings on the pilot mixture needles.

I ordered a pair of o-rings for the mixture needles and also new o-rings for the floats. Today I am going to pull the tank and pull the carb covers and re-seal that broken-off vacuum port on each one, plus make sure the slides are not sticking (wouldn't that be a kicker ...). With any luck I can get it to run well enough to ride a bit until the o-rings come in and maybe by the weekend I can take it apart and replace the o-rings.

I have a MSF course coming up in abut 10 days and I have ridden maybe 30 minutes on this bike, the only riding I've done in 20 years. I need it to run well enough to get a little practice operating the controls in before the MSF course. It's a bit scary riding a motorcycle that tries to idle at 4-5K rpm! The minimum speed in gear is like 30 mph! Right now it will run and idle (mixture needles set 1/2 turn out or less) but it wants to stall so I have to blip the throttle when it's sitting still. I think that's good enough to practice riding but not good enough to leave the neighborhood.

[qcbaker]

...

I have a MSF course coming up in abut 10 days and I have ridden maybe 30 minutes on this bike, the only riding I've done in 20 years. I need it to run well enough to get a little practice operating the controls in before the MSF course. It's a bit scary riding a motorcycle that tries to idle at 4-5K rpm! The minimum speed in gear is like 30 mph! Right now it will run and idle (mixture needles set 1/2 turn out or less) but it wants to stall so I have to blip the throttle when it's sitting still. I think that's good enough to practice riding but not good enough to leave the neighborhood.

Well, it sounds like you have a better idea of whats going on in the carbs than I would lol. As for your MSF course, are you taking the Basic or Advanced course? If you're taking the Basic course, a lot of places will have bikes for you to ride there. I think the Advanced course you have to take your own bike, though.

[mr72]

I'm taking basic, and they provide motorcycles. But I just need to retrain my hands and feet to work correctly on a motorcycle. I found my muscle memory was confused after 20 years of avid cycling, so I just need to get some parking lot minutes in, get the coordination of my hands and feet back where they were when I was a kid.

[qcbaker]

I had a similar experience when I bought my GSF. I rode dirt bikes every summer for like 8 years when I was younger. I hadn't ridden for about 6 years when I bought my GS, and my first time pulling off from a stop was a bit jerky, but I didn't stall or drop the bike. Felt like I just needed to remind my hands and feet how to operate the bike, then after a couple rides I found that I got back into it pretty quickly. Once you fix up your gremlins, I'm sure you'll get back into the swing of things fairly quickly. It's like they say: "you never really forget how to ride a bike" lol.

[mr72]

Well my problem is that for the 20 years while I have not been riding motorcycles I have been riding bicycles, mostly mountain biking, like 5-10 hours a week. So my hands really think they know what they are doing, but they are trying to do two incompatible things... grab all the lever with your left hand at a stop, which you'd NEVER do on a mountain bike unless you really are in love with that head injury, and the dive you get from pulling the right lever just feels all wrong. It'll just take me a few miles to get it back into the groove.

It's kind of like trying to drive a RHD car on the left hand side of the road.

[mr72]

Last night I worked on this a little more.

I tried spraying carb cleaner all over the carbs, intake boots, etc. to see if a vacuum leak would reveal itself. It didn't.

I noticed there was no cap on the right carb vacuum port, and I know it's supposed to be internally blocked off but I went ahead and put a cover on it, which didn't help.

I am about sick of taking this tank on and off! It's a huge pain to get the bolt holes to align to get it back on, since most likely one of the POs bent the bracket. But it's coming off again, because again I think there HAS to be a vacuum leak somewhere causing this issue. So I'm going to give it one last ditch effort to repair.

I ordered o-rings for the floats and the idle mix needles, after finding an amazingly cheap source. They are on the way. Hopefully they get here by the weekend so I can get the bike together and try it when I have some time.

I didn't investigate whether the diaphragms are leaking or whether the slides are working. I think a leaking diaphragm would have the opposite problem ... the bike would not want to rev UP from idle. But a sticking slide (or two) might cause the hanging idle, no?

Also, someone has put goop of some kind, like epoxy maybe? all over the attachment points of the little brass tube on one of the carbs.... the part you see here to the left of the vacuum port and throttle shaft:


I imagine they put the goop on there because there was a leak. Is this vacuum or fuel?

So here's the current condition:
There is some elusive set of mixture/idle adjustment conditions wherein the bike will idle with the dreaded "hanging idle" symptom. When set like this, I still have to nurse the throttle to keep it from dying.
Much more common is the condition where it won't return to idle. It hangs up at like 5K and won't idle down on its own. You have to do something to force it like apply the choke briefly or (presumably) let out the clutch a little to try to stall it.
OR I can set the idle lower and it won't hang up at 5K but instead it just won't idle, it dies if you don't constantly hold the throttle open a little bit.
We're talking like 1/8 of a turn of the idle speed adjuster difference between 5K-hanging-idle and won't-idle-dies.

Basically this is exactly what it was doing when I got the bike.

Since I discovered the missing vacuum port o-rings and replaced them, AND there was no real change in behavior, I think I can safely assume there is still a big vacuum leak.

My next move is to pull the carb caps back off and revisit the plugging of the vacuum ports (recall, they were broken off some time in the bike's history and a PO "plugged" the holes with some kind of goop like permatex). I figure eventually, if I can get the bike to run quasi-reliably and don't end up throwing it off a bridge somewhere, I should replace the tops but they are kind of expensive and something tells me I might have to replace the entire carbs. So I am going to just redo the plugging of these ports, hopefully do a better job and ensure there is no way they can still leak.

WHERE ELSE SHOULD I BE CHECKING FOR A VACUUM LEAK?

1. Vacuum ports (one on top of each carb, one on side of each carb [petcock])
2. intake boots
3. ?? where else?!?

[qcbaker]

I saw this while browsing the wiki, sounds kind of like some of the symptoms you're having

http://wiki.gstwins.com/index.php?n=Troubleshooting.BikeRunsBadly

maybe it will point you in the right direction.

[mr72]

I saw this while browsing the wiki, sounds kind of like some of the symptoms you're having

http://wiki.gstwins.com/index.php?n=Troubleshooting.BikeRunsBadly

maybe it will point you in the right direction.

BTDT ... a lot.

I cleaned the pilot jets manually and replaced the mains.

I have a new set of pilot jets here and I think I'll replace them for good measure when I have the carbs off again probably this weekend.

[crazydred]

Since I read your post quite fast I did not notice if you checked that the left carb vacuum port is capped where a hose would connect to the original petcock.

Good job fiding that those 2 little o-rings on top were missing.

I also capped the right carb vacuum on my bike just for good measure 


Do you get RPM fluctuation when you stop at a traffic light for example?

Quick tip: When diagnosing I like to have the bike on the center stand (horizontal)

[crazydred]

Inspect the intake boots, if the rubber is dry you can have a leak there.

Do not put your tank on and off (I have done that about 10 times last month), find a way to feed the bike with fuel. With a small bottle or so connected to the carbs fuel line.

Start your bike without the airbox with a bit of choke since she will not run without choke this way, listen to the engine running, are there any RPM changes?
Spray break cleaner to the intake boots -> RPM changes?

Go ahead and make yourself a simple tool to equalise your carbs (with the airbox!) just for good measure. If you can't equalise there is a leak somewhere
( careful since the leak could be in your equalising tool!! been there done that ahah)

With patient and persistence you will fix it! 

[mr72]

Since I read your post quite fast I did not notice if you checked that the left carb vacuum port is capped where a hose would connect to the original petcock.

I didn't bother to update, but it appears the original petcock was put back and actually working properly, except that the PO had put vinyl fuel hose in place of the vacuum hose so it was quite obviously not only leaking but incapable of holding a vacuum. I replaced the hose.

Good job fiding that those 2 little o-rings on top were missing.

Searching this forum showed me where to look. However, I think this still may be the cause of my vacuum leak because of a crummy job sealing the remnant of the broken-off vacuum ports.

I should take a picture and post it, where the vac ports are broken off and sealed off. It's going to make balancing the carbs a little more tricky. I'm gonna have to use my old uni-syn.

I also capped the right carb vacuum on my bike just for good measure 

While I have the carbs off next time I think I'll tap the hole and put a screw in it with blue loctite just to make dang frikin' sure it doesn't leak. Or maybe I'll just fill it with JB Quik.

Annnd... searching the internets popped up some kind of good ideas on sealing vacuum leaks on stuff in CV carbs bikes, like painting rubber parts that may have stretched or may have tiny surface cracks with plasti-dip, such as the intake boots. I figure these must be easy to get off of there anyway once the carbs are off so I will likely pull them and check to make sure there's not a leaking o-ring or cracks.

Do you get RPM fluctuation when you stop at a traffic light for example?

Well, I'm not riding the bike. I've only actually ridden it maybe 20 minutes total since I got it, and not at all since I put the carbs back over the weekend. This is because of the inconsistent idle.

But it doesn't seem to fluctuate. It either will be hanging idle that delays to rev down, or if I enrichen the pilot enough to prevent that, then it can't be set to idle other than 4-5K rpm or too low to keep the bike running.

Quick tip: You can check for air leaks by spraying brake cleaner to the carbs while the bike is running. If RPM changes you have a leak.
When diagnosing I like to have the bike on the center stand (horizontal)

I did this, of course, with carb cleaner and not brake cleaner. There was no leak evident. I may try it again, being more attentive around the intake boots. Would be way easier if the bike were elevated 4 ft. in the air

[crazydred]

Do you get RPM fluctuation when you stop at a traffic light for example?

This is because of the inconsistent idle.

But it doesn't seem to fluctuate. It either will be hanging idle that delays to rev down, or if I enrichen the pilot enough to prevent that, then it can't be set to idle other than 4-5K rpm or too low to keep the bike running.

If the RPM does not come down from 4k you have an air leak, on my case the airbox was no connected properly to the carbs!


Post a picture of the broken carb top

[mr72]

Inspect the intake boots, if the rubber is dry you can have a leak there.

Right, that's one thing I have not yet checked.

Do not put your tank on and off (I have done that about 10 times last month), find a way to feed the bike with fuel. With a small bottle or so connected to the carbs fuel line.

Good idea.

Start your bike without the airbox with a bit of choke since she will not run without choke this way, listen to the engine running, are there any RPM changes?
Spray break cleaner to the intake boots -> RPM changes?

Another good idea

Go ahead and make yourself a simple tool to equalise your carbs (with the airbox!) just for good measure. If you can't equalise there is a leak somewhere

I have (somewhere in my collection of vintage tools!) a uni-syn carb synchronizing tool. I just have to dig it up. But I need to get the thing basically running right first. Since the carb-sync vacuum ports are broken off/sealed up from my carbs, the preferred simple method to balance them is not available.

With patient and persistence you will fix it! 

I'm pretty confident of that. It's just whether I have a sufficient quantity of patience and persistence to invest!

If the RPM does not come down from 4k you have an air leak, on my case the airbox was no connected properly to the carbs!

I can see how that's highly possible, but in my case I attached the carbs to the airbox before fitting the carbs to the intake boots, so I am 100% sure they are completely and fully connected. But I suppose it's possible I have a crack or air leak in the airbox somewhere, such as the interface between the rubber air horns and the air box. I intend to eliminate this possibility in the near future with pod filters.

Post a picture of the broken carb top

Will do. In fact, it turns out I have the evening to myself today after work so I might actually dig into this yet again. I'll take the time to take pictures.

I still think there's one or more air/vacuum leaks that is causing ALL of this trouble. With 25-year-old rubber parts, it's not surprising. But it is a huge PITA to track down.

[crazydred]

Well I must say that your bike is older than me and I would be glad to see it running properly again ahaha 

When you post some pics we can analyze the damage

[mr72]

Well I must say that your bike is older than me and I would be glad to see it running properly again ahaha 

It'll be running properly again eventually, that's for sure.

I mean, I have been working on cars and small engines for far longer than this bike has existed. First motorcycle I nursed back to functional state from non-running state was a mid-70s Yamaha DT80 that I fixed when I was 12 ... that was 1985. The next summer we resurrected a 70s Honda Z50A, well sort of, it was missing the right side engine cover and we never replaced it. But boy did it run. And throughout my teens and 20s I did lots of work on carbureted cars including my 240Z and a couple of VWs my brother had and some friends' Z cars. ... and I think I've worked on countless weed eaters, lawn mowers, leaf blowers, chainsaws, mini-bikes, go-carts, engines bolted to bicycles, mopeds, you name it. Guess I always had a knack for this and I've been at it for three decades.

I'll get it eventually. Just need the collective here to help me skip a lot of steps. It took me a month of daily tinkering to get that DT80 running nowadays I'm not some kid on summer vacation where I can go tinker with something all day every day for a month. I need to get this bike working right in hours, not weeks or months. And I think that's even possible!

[mr72]

OK this evening's update.

I took the carbs off after running the bike out of gas with the tank and airbox off spraying carb cleaner over everything trying to find a vacuum leak where none could be found.

Took the carbs apart again and here's what's up, so far.

- the o-rings on the mixture needles were shot. Both are flat as a pancake. New ones on the truck.

- the boots connecting the carbs to the engine are in mint condition. No way they are leaking. They are perfect.

- the carb tops where the vacuum ports are broken off... first I inspected the broken off spot where the holes were filled in. Looked like solid work. Then I poked a screwdriver through the "goop" that had filled in the holes, and lo and behold, it was some kind of ... wax? grease? who knows. Somewhere between old grease and wax. About the consistency of peanut butter. NOT GOOD. I cleaned the holes out really good, put a piece of masking tape on the inside and then filled the holes with JB Clear epoxy.

Carb tops with original goop:


Carb tops with epoxy setting up:


- ran a 0.013" guitar string through most of the orifices and channels of the carb and sprayed everything with carb cleaner. Carb looks to be good to go besides the float o-rings, needle o-rings, and of course that disaster of broken off vacuum ports.

I actually feel good about it now. I inspected the carbs and couldn't find anywhere else that a leak may be happening. Everything seems to be working fine. One of the diaphragms looks a touch dodgy but no pinholes or other issues. Slides move like they should. Needles are fine. I replaced the old (new looking) pilot jets with a new pair just for good measure. Should get the o rings by the weekend or so and be able to put it together and see how it runs. If it doesn't run mostly right after this, then I will be truly lost.

Truly I think 99% of the problem was the waxy goop in the vacuum ports, and the other 1% was bad o-rings on the mixture needles. Getting rid of the airbox in favor of pods will just remove chances for stuff to leak and make assembly far easier.

[crazydred]

Good job man, you are going the right way 

[mr72]

I got everything back together and I am back to the drawing board.

Replaced all of the carb o rings, intake boot o rings, thoroughly cleaned the carbs and set the float height. Put in 40/127.5 jets. Set the idle mixture to 2.5 turns out. Left the stock air box.

Bike started fine and warming up in the garage seemed to run great. I thought I had fixed it. Then I rode it and the idle was hanging up at 3k. I can't adjust it so it doesn't hang at 3k without being too low to stay running. The idle is not really consistent.

Finally I started toying with the idle mix and now it won't start when hot. I am going to set it back to like 3.5 turns out once it cools and try again. I managed to get it running well enough as long as I nurse the throttle when stopped. I am close to thinking that's as good as it will get.

Ideas? BTW I am absolutely sure there is no vacuum leak. And I hate carburetors.

---EDIT---

Well, after sleeping on it and mulling the problem most of the afternoon yesterday I think the problem is that I might have had the mixture nearly spot on but then I adjusted it too far. And maybe the carbs need balancing and the valves need adjusting and I just don't have patience to do that all right now, while I do have patience to ride it with a slightly iffy idle.

So I set it back to 2.5 turns and when I get to ride again I'll set the idle speed so that it requires the occasional throttle bump to keep running and then leave it alone until I can make time to adjust the valves and sync the carbs and then see if I can make finer adjustments to the low-speed mixture to get it to idle better. Right now this bike with 20K miles on it has just too many little things that have been neglected, I am afraid I probably can't get it perfect with just the carbs.