A journey through a hanging idle.

Greetings,

I'd like to start a thread on the issue of my bike starting to develop a hanging idle as the season comes to an end.

The carb/intake/exhaust story goes like this: I bought the bike stock last september. Did the standard maintenence while keeping everything stock: Valve shim adjustment, zestful cleaning of carbs, including breaking the rack and using new throttle shaft seals and fuel rail o-rings, etc. Followed up with a bench sync and then a two bottle vacuum sync. At this time the fuel mixture screws were soft seated and backed out to 3/ 1/2 turns each.

Two disclaimers: I did not set the float height, I did not use a YICS blocking tool, and I did not use a colortune.

The bike ran quite well after all of the standard maintenance. (though it was winter, so I did not actually ride it).

At this point I started to tinker, and put on pods using the stock airbox to carb boot instead of what came with the pods.

I went up to a 124 main, and used two tiny thin washers to raise the needle.

I also lost the exhaust collector because it was completely rusted.

By this time, it was spring/summer so I actually got to start riding the motorcycle with the new mods: Pods, open headers (not by choice) slightly raised needles, and 124 mains. It ran well, though just a tiny bit lean (some popping on deceleration). I kept an eye on it and the plugs were ok. I then added a stock exhaust collector and while it actually did run even better (and a tad bit more rich) I started to notice a bit of a hanging idle.

The idle works like this: I pull the clutch in to shift, and the RPMS don't drop. Not as much as they should, at least. This is most noticeable when I pull in the clutch in second gear coming to a stop (if I weren't to downshift to first). The RPM's don't drop until I start to move very slowly.

I've always felt like it was a clutch issue, but I've adjusted it so many ways I just don't think it is (even though at times I will slip after 6k in 3rd or 4th gear, when I'm toying around and trying to find the sweet spot).

At this point I pulled the carbs and polished the slides and bores, just to be sure. Still hasn't helped. I really don't think I've ridden enough to have my valves out of spec again, but its a possibility. Tonight I vacuum-synced the carbs so I'm going to take a ride tomorrow and see if that helps at all.

My next step is to back out the mixture screws another full turn to 4 1/2 out. I also ordered a colortune to test out. I'd like to get this sorted out before winter when I pull the motor for cleaning and frame paint, so if anyone has suggestions after this wall of text, I'm all ears. I have no problem messing around with these but some criticism and help never hurts. So lets talk it out!

pic for clicks:

 

Could it be as simple as a worn throttle cable, or one in need of lube? Before we open the "Pods and exhaust" can of worms again?
As for slipping clutch, what oil are you using? Has it ever been rebuilt? Getting the basics out of the way!

ps I love the look of your bike.
pps thought of a thread in "Other Bikes" for that olive cb550f? I'm a Honda junkie! I need about 3... 70s cb4, 80s cbx, pre 82 goldwing.

 

Does it hang high when warm and in neutral? That would be an easy way to check whether your clutch has anything to do with it.

 

I am watching this as my high RPM issue has returned, but very sporadic.
Can you expand on the warm engine, clutch and neutral condition?


Brosef your bike looks great in fall colors.

 

..sometimes if idle circuit is up to high..my bike won't stop climbing revs; until i go to neutral often i can't even pull in clutch at bars due to excessive rev climb..turning lower the {choke }is only way ..for me sometimes

 

Lean idle mixture can cause RPMs to hang high and only slowly return to idle. Actually, though, I was wrong. This is usually worse when cold. Trying it in neutral removes the clutch and drivetrain from the equation.

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

 

..is only when cold,and I'm jumping out so i won't get at the neighbors n their evil sides ..yes i understand the concept of neutral..my instance involves when i slow .if i pull in clutch @h.bar my revs go way over..until i get my shift on into neutral.then she goes way back down..

 

Well, if it's not hanging high when revved in neutral, then it's probably not a carb problem.

 

I'll answer everyone in order. New to "quoting" so bear with me here.

MattiThunder

Throttle cable is new, and I've left plenty of slack to be sure that it's returning fully. That said, I'll relube it to get that out of the way.

I am using Valvoline 20w50 four stroke motorcycle oil. Says it offers "superior wet clutch protection."

Thanks for the compliment. I thought I did start a thread for that CB (750k, by the way!) But if I haven't I'll do that shortly.

SQL

When warm, and in neutral, if revved to say, 3500, yes, it does hand a bit before dropping back to idle. I noticed you may have contradicted yourself a little on the cold vs hot issue. The revs acvtually don't hang much (if at all) when cold and revving in neutral. The problem gets worse when warm.

Working from home today, and since I synced the carbs last night I'm going to take the bike out for 30 minutes and see if that helped at all. Will report back around 1.

Thanks for the compliment stump.

 

Sorry, i was confusing you with another member that just got a 70s 550f in gorgeous olive green. I wanna see builds for them all! I remember yours from the basement pics now. I got to get me one ... almost thinking of selling the xj for one. Don't tell the group!

 

Hm.

It seems I didn't do a very good sync, because the number two cylinder didn't start firing until about 10 minutes in. After that it ran well, (though I didn't really give it a long enough ride to check that hanging idle. But I've NEVER had the cylinder not firing problem before just now. Looks like I'll be back at it with the two bottles this evening. Am I right in doing the sync this way: Sync one and two by using the screw in between the one and two carbs. Then sync two and three with the screw in between the 2 and 3 carb. Finally, sync 3 and 4 with the screw in between 3 and 4?

 

From what I remember (I no-longer have a 4-carb bike), the easier method is to synch 1 to 2, then synch 3 to 4, and finally synch 1/2 to 3/4 using the middle screw.

 

What do the plugs look like after idling a bit?

 

When the bike is hot or cold?

 

Warmed up to normal operating temp.

 

I'll get back to you on that around 5. I should also add that in addition to that cylinder being off until the bike gets warm, I did notice a bit of popping on acceleration and that's never happened. It used so pop ever so slightly and infrequently on decel, before I re-synced.

I also found out that I synced wrong. I did 1 and 2, then 2 and 3, then 3 and 4. Oops, I forgot from the last time I did it.

I have confirmed that I need to do 1-2 then 3-4 then 2-3 since I'm using this two bottle method.

 

Real time updates here. I Re-synced the carbs. Going from 1 to 2, then synced 3-4, and finally synced 3-2. Then, I unscrewed my air/fuel mixture screws 1/4 turn before I went another another ride around the neighborhood.

Now, not only am I still getting the stuttering from 1500 to 5/6k rps, but my idle is sitting at 1500 (and I have the idle adjustment knob backed allllll the way out), still with a hanging idle! I'm so confused. I'm going to screw the mixture screws in back to where they were (3 1/2 turns out) and take another ride.

In the meantime, this is what my plugs look like when I pulled into the yard and turned the bike off.

1 2 and 4 all looked like this:

and 3 looked like this. Note how white it is (with a touch of brown on a spot) and how the ceramic is also chipped? Never seen that before.

 

OK. So, no fuel coming through the #3 carb. You may be getting some fuel into #3 through the YICS passage. Need to find out why that carb is not delivering fuel... unless there's something really wrong with that cylinder, like a bent valve. Have you checked compression? Coincidentally(?) #3 was the one that had a bent intake valve and only 30 PSI compression on my GPz 750 when I got it.

1, 2, and 4 show plenty rich.

High idle with idle screw leaving the butterflies closed certainly sounds like there's an air leak somewhere.

Edit: Have you verified that you're getting reliable spark on that #3 plug. If there's no fire, that would be another reason for it to show clean vs. the rich of the other 3.

 

I haven't, but it's something I'll do for peace of mind. I really don't think that's the issue though, because everything ran well and I wasn't having any misfire issues (I haven't had an issue all summer) until I tried to re-sync last night. I wish there wasn't so much conflicting information on syncing the carbs with two bottles. Now I'm reading that I need to do 3-4 first, then 1-2, then 2-3. So, here I go. I'll also check spark on 3. Will report back in a bit.

For piece of mind i think Im going to buy new vacuum port caps tomorrow.

 

The two bottle method should give good results, unless a vacuum port is partially or totally blocked, but I wouldn't see how it could he possible...