Topic: Hanging idle....I'm done

[Scott S]

 The exhaust in the video? Stock 4-4 pipes.

[Korven]

The exhaust in the video? Stock 4-4 pipes.

Ment the 4-1 exhaust on first page of this thread.

[Scott S]

The exhaust in the video? Stock 4-4 pipes.

Ment the 4-1 exhaust on first page of this thread.

 Found it on ebay. Don't know the manufacturer.

[Scott S]

 I pulled the carbs the other day and set the slides back closer to the stock setting. One thing that's always bugged me about the 49mm is that the main idle screw is WAY in. If you look at some of the pics and the vid I posted (on page 3, I think), you can see that the spring on the main idle screw is completely compressed.
 I have some pics from when I got the bike. It still has the yellow paint marks on the sync screws and the idle adjustment screw is about halfway through the travel.

 I'm beginning to think that it's the O-rings more than anything else. My carb guy uses some unknown brand of O-rings. I swapped those out for the ones from Hondaman and, honestly, they might be even more loose now.
 I am going to order some new main jets/O-rings and see if I can tighten up the fitment.

 That means the carbs have to come off AGAIN....argh! I will say, I've started using a method similar to the 550 assembly manual, posted in a sticky on this site. I loosen the electrical panel on the LH side of the bike and let it hang out of the way. I remove the battery and battery tray completely. I remove the air box completely.
 Using this method, I had the carbs out, adjusted, and the bike back together and running in about 3 hours the other day.

[grcamna2]

Scott,have you serviced the advance mech ?

[Scott S]

Scott,have you serviced the advance mech ?

 Not yet, but I'll check it. That didn't fix it the last 3 or 4 times, though.

[HondaMan]

 I'm beginning to think that it's the O-rings more than anything else. My carb guy uses some unknown brand of O-rings. I swapped those out for the ones from Hondaman and, honestly, they might be even more loose now.
 I am going to order some new main jets/O-rings and see if I can tighten up the fitment.

 

Hmm...this sounds like the holes eroded some, probably in what I think of as the "1980s cycle". I've seen several CB500 carbs sets that had larger-than-normal holes and I had to use larger-than-normal O-rings on its jets. The issue was that the carbs had sat until dried out multiple times with MTBE gas in them, and then several times someone (before I got them) had replaced the O-rings on the mainjets, polishing the holes a little bigger.

Which size did I send you? I have slightly larger ones, too. I could send those, if I find out which ones I sent last time?

[Redline it]

not to get far off track, as much as i have been in the last couple years. i picked up xr650r 2000 in pretty good shape, it's all i do now days is ride that. and hanging idle could be a different game all together for the cb's and xr's, but this beast i ride has to be set perfect no matter the stage of wear, or the state of other adjustments. the slide has to be at the bottom and the air pilot jet screw has to be perfect set with the slide, although it can be a little off and you can dial in the idle screw or not but it'll drive you crazy trying to get it right. for starting the choke is determined by temp of course and jets, needle, but it's so precise, that almost any slight differences are gonna mess with you. so starting it with no throttle, if the slack is slightly tight, it'll sneek  up on you and start hanging. reaching down the idle screw which is upside down so you gotta think which was it is but as soon as you give it some slack the hang is just micro seconds. the thing to do is set it just like the factory settings according to altitude and go from there, if that pilot jet was put in and the oring got sideways, it'll not work, but if it's working, adjust it to run fat side, so it seems it's way dependent on throttle cable slack now. gotta have just the right amount: too much and there's a slight hesitation and that's not good because it'll try to face plant you forward and you need exact response so it handles like a cadillac. aircleaner has to be clean, although even riding alone the thing creates a dust storm at the airbox, anyways, hopefully that sheds some ideas from a different side. i still ride the 400f hard as i can. just now after a couple years on a top end job it's starting to leak at the left valve cover corner. seats still only last 2 or 3 years tops. are you sure those little kehin spring loaded ball sockets are in right and not binding? or the main return spring? cables are mounted right and not pinched? i know you know, i just wanted to say hi to y'all. i miss being here as much as before...oh i just about had a 65 650 TR-6 special with barely any miles on it with all original parts, running,  a spare bike with it, belonged to my cousin, he husband killed himself early 70s, for 10k. she backed out and is gonna give it to a grand daughter that's she's never met, when she dies, because the girl's husband wants it. jesus man. i was on my way to pick it up. i was gonna put em both in the living room to do some prep work. it's got some scuffs on it is all. nobody on that side has any idea how to set it up or maintenance anything. it hasn't been ridden since the 70s. well keep having fun. ride as hard as you can.

[Scott S]

 Pulled the carbs again yesterday. The last couple of times I've pulled them, I've been using a method based on the 550 Assembly Manual sticky posted here. I remove the battery/tray, hang the electrical panel off the left side, and completely remove the air box. It sound like a lot of work, but it makes it SO much easier to get the carbs in and out. The last few times I've done it this way, I've had the carbs out, adjustments made and bike back together and running in about 3 hours.

 Since the last time I "cured" this issue was by using aftermarket main jets with snug fitting O-rings, I ordered a set of 100's. When I got the carbs open, I realized that the Hondaman O-rings fit the best of anything I have. They are all snug and tight and I don't think they are leaking by. I also checked the float heights and they're all good.
 These carbs are super clean. The emulsion tubes will drop right out, all brass is genuine Keihin, etc.

 Pulled the advancer and checked/cleaned and lubed it. I put a drop of 3 in 1 oil on each post where the weights attach. Cleaned the cam lobe inside and out and put the thinnest smear of brake part lubricator grease on it. The springs felt great. I've had worn out springs before and these snap back nicely.

 Reassembled the bike and ...yep... still hanging. I figured I'd try a vacuum sync and see what happens. That did seem to help a little, but not cure it completely. Then the throttle cable started getting hung up.

 The cable hasn't been an issue, and I lubed it at both ends with a couple of drops of 3 in 1 oil. When the cable came out of the adjuster at the handle bar end, the outer sheath frayed a little. That is causing an issue now.
 I found an aftermarket cable in my stash and will swap them out and see what happens.

[seanbarney41]

Guessing you have tried this, but I just had a mysterious hanging idle on a fresh built cb750.  Air screws fixed it.  Somehow during start up up and adjustment I had them more than 1-1/8 out.  Set 'em to 3/4 turns out and bam...fixed.  I know the settings are different for the 500.

[grcamna2]

Pulled the carbs again yesterday. The last couple of times I've pulled them, I've been using a method based on the 550 Assembly Manual sticky posted here. I remove the battery/tray, hang the electrical panel off the left side, and completely remove the air box. It sound like a lot of work, but it makes it SO much easier to get the carbs in and out. The last few times I've done it this way, I've had the carbs out, adjustments made and bike back together and running in about 3 hours.

 Since the last time I "cured" this issue was by using aftermarket main jets with snug fitting O-rings, I ordered a set of 100's. When I got the carbs open, I realized that the Hondaman O-rings fit the best of anything I have. They are all snug and tight and I don't think they are leaking by. I also checked the float heights and they're all good.
 These carbs are super clean. The emulsion tubes will drop right out, all brass is genuine Keihin, etc.

 Pulled the advancer and checked/cleaned and lubed it. I put a drop of 3 in 1 oil on each post where the weights attach. Cleaned the cam lobe inside and out and put the thinnest smear of brake part lubricator grease on it. The springs felt great. I've had worn out springs before and these snap back nicely.

 Reassembled the bike and ...yep... still hanging. I figured I'd try a vacuum sync and see what happens. That did seem to help a little, but not cure it completely. Then the throttle cable started getting hung up.

 The cable hasn't been an issue, and I lubed it at both ends with a couple of drops of 3 in 1 oil. When the cable came out of the adjuster at the handle bar end, the outer sheath frayed a little. That is causing an issue now.
 I found an aftermarket cable in my stash and will swap them out and see what happens.

Scott,at the bottom of your second paragraph you said that "the emulsion tubes will drop right out,".. 
I know they need to be a tight fit when they're installed;they all need to seal tight and 'seat' into the carb. bodies,other wise they will allow fuel to seep past them,rather than pull 'only' through the center holes and around the needles with those needle jets.
I had some like that and was able to carefully wrap a thin piece of teflon tape at the tops of the needle jets/emulsion tubes where it meets the carb. bodies which cured the problem.
Do your emulsion tubes/needle jets look worn ?

[Scott S]

 No, they don't look obviously worn. What I mean is that I have had some that were so cruddy I had to use a wooden skewer to wiggle them out. These are very clean.

 I did have a 550 once that had worn emulsion tubes/needles. It didn't have a hanging idle, but it ran pig rich. Only new jet sets (emulsion tube and needle) cured it.

[grcamna2]

No, they don't look obviously worn. What I mean is that I have had some that were so cruddy I had to use a wooden skewer to wiggle them out. These are very clean.

 I did have a 550 once that had worn emulsion tubes/needles. It didn't have a hanging idle, but it ran pig rich. Only new jet sets (emulsion tube and needle) cured it.

How do those emulsion tubes fit in their respective bores in the carb. bodies ?

I imagine if they were loose in there,you would see the plugs to those ones a bit darker than the rest..

[Deltarider]

Scott,at the bottom of your second paragraph you said that "the emulsion tubes will drop right out,".. 
I know they need to be a tight fit when they're installed;they all need to seal tight and 'seat' into the carb. bodies,other wise they will allow fuel to seep past them,rather than pull 'only' through the center holes and around the needles with those needle jets.
I had some like that and was able to carefully wrap a thin piece of teflon tape at the tops of the needle jets/emulsion tubes where it meets the carb. bodies which cured the problem.
Do your emulsion tubes/needle jets look worn ?

My emulsion tubes always came falling down after the main jets were removed and I opened the throttle real wide. I don't see a problem with that as long as the O-ring around the main jet is OK and seals well. Bike pulls like a rocket and plug noses indicate a normal combustion.

[HondaMan]

This is just a hunch: close the idle-air screws down about 1/8 turn each from the stock setting. If it helps, I might have an idea 'why'.

[RAFster122s]

Any updates Scott

[Scott S]

 I haven't touched it.
 
 In response to Hondaman, I did play with the mixture screws. Made sure they were set to spec, then adjusted while the engine was running. I can't remember where I ended up, but they were closed a bit more than stock.

 What's your hunch?
 

[Scott S]

 Tried swapping cables today and the one I had is too long. Guess it's from a different model.
 Tried to trim the frayed sheath but the cable just doesn't act right. Time to find a replacement.

 Hondaman.... I checked the mixture screws and had them at 1 turn out. Set them at 7/8 and will try again when I get a cable.

[Scott S]

 Hold up! I may have good news to report!

 Dug around and found a cable that fits (wish the adjuster was chrome, though ... 😞 ).
 Installed, set the mixture screws to 7/8 and fired it up. The screws are at half a turn out, which I know isn't correct, but that's where it runs best. Even the width of the slot more and the hanging wants to return....though very slight.  In even a skosh and it wants to load up and bog at idle.
 
 I'm running a UNI filter. I wonder what a paper filter would do?

[HondaMan]

I'm running a UNI filter. I wonder what a paper filter would do?

Umm...that was my hunch.
I "fixed" both a 'CB500-2' (the 500cc version of the venerable CB450 Twin) and a CB500-4 that had foam filters when they came here, struggling to get ANY kind of idle, or else they would just hang at 1500-1800 RPM - but removing their foam air filters (both UNI brand) and sending them home without them, to get paper or K&N versions. Both would not respond with any semblance of normalcy at idle (or hot start for the twin) with the Uni filters aboard. This also happened here with a hotrod XL250 that came to me after being at 8 other "tuners" with a similar problem that turned out to be: a Uni air filter. After I fixed THAT one the guy mailed me a $50 tip(!) one week later: he'd been fighting it for almost 2 years, poor guy.

Perhaps I should explain a little:
The Uni filter foam is an excellent filter for engines that have a properly-sized version of it (as in, LARGE) attached, or if the engine doesn't supply constant intake suction (i.e., they are best on pulse-suction intakes). BUT...the stock air filter boxes on these bikes were sized for PAPER filters, which have a much lower density that does the Uni foam, so while the paper (and gauze versions like K&N) can pass bigger particles of 'dirt' than the Uni type, they also drop the air pressure less than a foam element - a LOT less. Keep in mind: the paper or K&N gauze surface area is almost 8-10 TIMES as much as the surface area of the Uni, so the Uni is a much SMALLER air filter in the [same] space. Before Uni's foam came out there were other foam types and they all had a similar issue, not quite as pronounced, but they also did not filter to the small particle sizes that the modern Uni types do: they were less effective at trapping atom-sized dirt. They could be washed & re-used, so they got popular (more often on singles and twins). So could the K&N, in those bikes where it was built to fit into the airbox: the K&N gauze contains more surface area than even the OEM paper types, so it doesn't suffer the restriction problems.

It takes significant restriction to cause a fuel-mixing error, but it most affects the low-speed fuel circuit mixture because this is the more tentative mixing in these carbs: it happens as a timed-pulse-suction moment on the idle fuel jet, which has to lift the fuel from the fuel level in the float bowl all the way up to the throat of the carb on every intake suction stroke until about 1800 RPM - then the inertia of the fuel holds it more steadily in the carb throat. When the foam filter is 'sucked on' it will also compress slightly, causing more restriction, and thus the increased vacuum pulls more fuel up into the throat than should be there. This compression is what traps the dirt into the filter's oil, and it works well on pulse-feed engines like twins. On Fours not so much: the air intake thru the airbox is pretty steady, so the foam squeezes tighter than at rest, and the restriction rises too quickly. This in turn causes a [significantly] lower air pressure in the venturi, sucking up more fuel thru BOTH jets when the mainjet should not even be involved yet. So, Idle becomes really, really hard to adjust because the whole linearity of the low-speed mix has been 're-curved' from having a too-low air pressure on the airbox side of the slide.

You can test for this by removing the foam element, then attempting to run the carbs with their normal screw settings. Things should then be pretty normal up to about 1/2 throttle, when some restriction is expected [again] to match the lifting ability of the emulsifier tubes and their mainjet. Without a proper filter element at those air speeds the air tumbles more and this disturbs the laminar flow under the slide, over the top of the emulsifier tube. This then makes it run lean until about 3/4 throttle when it becomes essentially a lawn-mower carb, which is a fuel-metered hole that feeds any air that passes by. Then the airflow must be REAL smooth or it won't mix for beans, making the top end feel 'flat' despite proper jetting. This is then roadracer stuff (i.e., needs more air duct work), and the battles they fight: on the street we just see it as less/more passing power at high revs.