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...

 

#3 does not have a adjustment screw. It is adjusted by the throttle knob. The other three are being adjusted to #3.

1. Adjust 1 to 2.
2. Adjust 4 to 3.
3. Adjust 2 to 3. The #1 carb is linked to #2 and will be brought along with the adjustment.
4. Adjust the throttle knob. This will open/close all four butterflies simultaneously. Hope this helps.

Gary H.

 

Yep, this is the method as described in the XJ manual.

 

i think the 1/2, 3/4 are interchangeable just so the idle is kept in check and 2/3 is last.
the shims under the needles might be part of the problem with the black plugs.
looks like Sunday will be nice enough to ride, would you mind a visitor?

 

Agreed. After he's done it a couple times with success this should make sense to him as well.

Gary H.

 

After that THIRD sync in 24 hours, it looks like everything is back to normal. Before I did the final sync of 3-4, 1-2. and 2-3, I seated the idle/mixture screws and pulled them back 3 turns. While the motor was warm, I took a quick ride and everything seemed back to normal (will know more about the plugs and hanging idle tomorrow).

I think that I was a little sloppy with the first two syncs in that on the first one, I did it completely wrong, and on the second, I was not patient enough to really watch the fluid for a long enough time.

After I take a ride tomorrow, for the hell of it, I'm going to pull a washer off of the needle, leaving it at one instead of two to see what kind of difference, if any, that makes.

Also, yes there is spark to the #3 plug.

It looks like I need to get some NGK plugs, just for piece of mind. That broken piece of ceramic is unsettling.

Polock, would love to finally meet you. I'll send you a message shortly to se if we can work something out.

As stated earlier, this is my current setup on the 1982 XJ750 Maxim:

124 mains
Stock Pilots
two washers to shim the needle and raise it.
Pod filters
Stock header to collector, no muffler.
idle jets turned out 3 screws.

 

SQLGuy, i could use a little help. I am in the Springs.

 

Back again. Haven't had a lot of time until the past day or so.

After posting the above specs:

124 mains
Stock Pilots
two washers to shim the needle and raise it.
Pod filters
Stock header to collector, no muffler.
idle jets turned out 3 screws.

I'm still having the same issue of a slight hanging idle, and an extremely lean third cylinder. I have not checked compression, but I DO have spark to it.

So what haven't I done that I need to do?

Check for air leak: Picked up a propane torch.

I'm also going to adjust the carb fuel levels and float settings, but before that:

I measured the valve clearances, and I'm wondering if this is part of the hiccup.:

Exhaust 1: Exhaust 2: Exhaust 3: Exhaust 4:
.22mm (lots of force to get in, so more like 21mm) .19mm .19mm Tight .19mm
Y275 Y290 Y255 Y260

Intake 1: Intake 2: Intake 3: Intake 4:
.11mm .15mm .15mm .15mm
Y290 Y290 Y290 Y280

Is this weird that none of them got tighter aside from Intake 1? And that Exhaust one is completely out of spec compared to the others?

Would you guys suggest me changing any of the shims besides Intake and exhaust one, since everything else is in spec?

Thanks everyone. I'm going to keep this thread rolling until we get sorted out.

 

If it has not been said before, when you use PODS you are in uncharted waters. The air box in these bikes were designed the way they are for a reason. With PODS, you play with variables until you get a result that you can live with.

I am looking to purchase another bike. When I see PODS on the bike for sale, I immediately click NEXT.

 

#1 exhaust is slightly out of specs (on the loose side) but intake #1 is still slightly in (but definitely on the tight side). So you should get a 280 shim for your #1 exhaust valve.

If your #3 cylinder is runny lean, it is obviously not related to your valve clearance on this cylinder,

 

HalfCentury,

I utilized pods knowing full well what I was in for. As the post said, everything ran great all summer using a setup that several others with pods and modified exhausts used, with no trouble. Since I developed the hanging idle I decided to basically do over the 3k mile maint while making sure I have no air leaks. If I have to play around with the jets again in the spring so be it, but before I put it away I'm going to take care of these valves and carbs once more. I rode this thing a lot over the summer and it may just be time for a tune. I'm simply posting my results as I go along and looking for insight along the way.

Tonight I'm bench syncing and going through carb three to look for any clogs, I'm also ordering a colortune. Could anyone tell me the proper plug diameter to pick up (10, 12, or 14 mm)? And do you guys recommend the Gunson or the Morgan Colortune?

Thanks!

 

14mm Colortune, and, they are all made by Gunson. Morgan is just one of the re-sellers of the Gunson Colortune.

 

Your vacuum sync needs the YICS tool. Performing a bottle sync without the YICS tool is a waste of time. Have you obtained the YICS tool since your initial post?

 

I have not, actually. That's a good call. I'll make or order one today.

Chacal, thanks for the tip sir. Will report back after setting fuel levels/changing the exhaust shim, vacuum syncing (with YICS), checking for leaks, and colortuning.

 

There is an ongoing debate about that issue. Several of us have been able to synch the carbs successfully without using the YICS tool, and without using any special tricks to compensate for not using the tool.

 

One thing that hasn't been explored. When you put the rack back together did you make sure that the carbs were all aligned properly, and that the throttle plates snapped shut with all the vigor of a mousetrap?

 

Nice phrase..k man.

 

Ok. Understood. As a suggestion, perform the sync without the YICS tool and when finished, insert the YICS tool and check the balance. That would convince me.

My contribution to the discussion is that after my bench sync, one pair of carbs was horribly out of balance. Even though the bike started and could run, it was not properly tuned. I used the YICS tool and the results after the carb balance were amazing. The bike was a rocket.

 

when i ride the bike there is no yics tool in it. That is how i want it tuned

 

Mine are balanced within the error rate of my manometer without using the YICS tool, and it flies like a rocket too.
Will the YICS tool help? Sure.
Is it worth using? Debatable.

 

I the point of balancing with YICS passage blocked is that the cross-connect of YICS will hide imbalances... and those imbalances may play a bigger role when under load and operating in different parts of the powerband than when you're doing a vacuum balance. The YICS holes are really small, so I doubt it has much effect at mid-band or WOT... other than adding a bit of swirl, but it can probably cover up a decent amount of imbalance at idle.

 

I don't use a YICS tool. Do I have one....yes. Do I know where.......no. Do I care.....yes because I wonder where it is. It's brand new and still in the packaging----I'd like to see it again, just to remember what it looks like.

Dave F

 

Yes, the PASSAGE holes that lead from the large YICS CHAMBER to the combustion chamber are tiny and are easily clogged by carbon deposits over time....the same type of carbon deposits you typically find within the chamber, on piston crowns, etc. Once the passage holes becomes blocked, then the entire YICS system fails to function at all, or, in a greatly reduced manner. Even worse, if only SOME of the passage holes are clogged, and others aren't, then you have a mis-balanced situation that robs a bit of power.

The clogged passage holes are the main reason why "it makes no difference" whether the YICS tool is used, or not. If the passage holes are sufficiently clogged, then they are ALREADY blocked-off and isolated from one another, thus acting just as a YICS tool does, and then the tool is not needed....the coked (carbon) deposits are doing the job for you!

Of course, it's also negating the YICS system, so you really don't have a basis for comparison of a YICS vs. a disabled-YICS system.

I find it surprising that YAMAHA never made the un-clogging of the passage holes a regular part of the tune-up/synch procedures. Or maybe they did in some tech service bulletin and I've never come across it.

BTW, these passage holes are much larger on XJ550 engines, and thus rarely ever get fully clogged. On the other YICS engines, the passage holes are incredibly small and need the build-up removed periodically.

 

What do you exactly mean by periodically?

 

Every time before you synch............

 

Omar usually brings his YICS snake to the carb clinics for whoever wants to have their YICS passagec cleaned out.

There, Matti ought like that one.....

Dave

 

Yeah, but the snake only cleans the CHAMBER (that's important, too, mainly to prevent the rubber seals on the tool from getting scarred or torn)....the passage holes are the small diameter holes that lead from the chamber to the mating passages in the cylinder head. Take a look at a set of YICS cylinders (jugs) that you have laying around.....they're about 3mm diameter (less than 1/8").

 

I've had the entire engine apart, and thoroughly cleaned the YICS passages and chamber, prior to synching without the YICS tool. I can't compare the result to a non-YICS XJ, but the engine behaves as well as any properly synched inline four that I've ever ridden.

I can also add that at 27,000 miles the YICS passages on my particular engine were coated with a thin layer of carbon; nowhere near enough to clog the passages. As with all things, your mileage may vary.

 

The YICS holes don't go to the combustion chamber. They go to the intake ports.

 

i think there's a lot of these motors out there with lumpy idles because the tool was used to sync them. then the mixture screws are spun around to try and get a good idle because the book says to use the tool to sync, so it must be the mixture. wrong answer, it's the sync tool. tune it like you ride it