Idle hovering - trouble shooting guide.

[The Buddha]

OK lots of people have been posting with this problem.
Here it is in the order of importance/difficulty.

0. Idle set too high: adjust idle to ~1200 rpm when bike is fully warmed
1. Air intake leak/missing O rings in vacuum circuit.
Test with wd40, locate it, confirm it, and replace the bad part. Intake manifold boots, O rings, caps etc etc going bad can do this.
2. Clogged up this or that. Yes obviously clean it and check it. You need gas getting to the motor nice and atomised and predictably and about equal from left to right.
3. Hanging cables. Choke, throttle etc ... have to open and close fully and have slack in them at close.
4. Of course you can also have a valve hanging open, as well as a leak at the exhaust causing these. Fix the leak, adjust your valves - use the kits that have been doing the rounds and the kerry DVD for it.

These 0-4 are a must, nothing else will work if these are bad.

The thing though is ... inspite of these being good, the idle can hover.

Other than some very rare cases, its usually due to the fact that the idle/pilot circuit is awfully lean from the factory.
That scenario calls for a swap to 40 pilots, 125 mains, and setting your mixture screws to 3 turns out. Synching the carbs, setting floats and overall rejet it to the right spot.
That is on an 89-00 bike. Newer years have the same problem, but slightly different jet numbers, but same concept. +1 on mains, needles and pilots, and + 1 turn on air screws as well as synch and check on floats.
Now I can rejet for y'all, or sell you the bits to do it, but I'd encourage everyone to do it themselves. At the very least you'd know what's going on underneath your butt. Make sure the shop's you buy from get you the right types of jets, like there is 5-6 types of mains, 5-6 types of pilots, just get the right kind for your bike.
Cool.
Buddha.

[beRto]

I would say #1 should be "Idle set too high: adjust idle to ~1200 rpm when bike is fully warmed"

[The Buddha]

I would say #1 should be "Idle set too high: adjust idle to ~1200 rpm when bike is fully warmed"

Edited to fit ... thanks berto.
Cool.
Buddha.

[theUBS]

Just to clarify for newbies like myself, since these bikes don't have temperature gauges.  I'm assuming after my recent experiences, that there may be a few minutes difference between these two states:

1.) holding a smooth unchoked idle, seemingly ready to ride AND
2.) full operating temperature?

[yamahonkawazuki]

well imho ready to ride, is after like you said, holding an idle. full op temp, i usually get that after a quick spin,, but not long after the initial warm up tho

[theUBS]

It took about a solid 10 minutes or so, be it idling or riding, for my hanging idle issue to show itself.  I'm assuming that's when it was fully warmed up.  I think I have it set just about right now.  Now, I'm just going out of my mind waiting on fresh tires to show up!

[The Buddha]

10 mins is about normal for it to get to temp. Theoretically you're not supposed to take off before that, and worse, do all your tuning in that temp.
However, a lean bike will get hotter than a rich bike, and will there fore misbehave much more till you get it to that temp ... if you tune it in the max temperature situation.
I just jet it to run right and you'll run cooler and reach the steady running state sooner. You are not ever supposed to take off with it cold cos oil may not have gotten everywhere, but 2-3 mins in, it should not be an issue. You're not supposed to stress the motor till it fully comes to temp, and that is that ~10 minute mark.
So, the right jetting will let you start it, 2-3 mins later take off the choke and ride off gently and then have your way with it ~10 mins. 2-3 mins of choke and then take off choke and ride. The right jetting will let you do that as well as not give you any trouble for hot, warm or cold restarts. Hot restarts no choke, the cold = choke, warm may need choke but can take it off in a few seconds. Also at idle the bike should stay just a hair lean. Else hot restarts will be harder. Jet it too rich and hot restarts will be difficult. In fact it may run like crap with it too rich as well. Especially idle. It will easily stall under braking etc etc ...
Cool.
Buddha.

[bval]

Thanks, Budda, for providing this thread.

Missing 0-rings are mentioned frequently and were recently a problem for me. However, which o-rings and exactly where they are located is often not specified. There are a few locations in the carb system that use o-rings, so I assumed the wrong ones for a while and wasted a lot of time troubleshooting. To help save othes the headaches, the typical ones that can cause idling problems are very small, (slightly smaller than the diameter of the eraser on the end of a pencil) and are trapped in a small circular recess on the top of the carb body between the body and the diaphram cover.

You may not even know they are there when you take the covers off because they can stick to the cover and fall off before you even know they exist. Some have said they are orange, but I wouldn't know as I never saw them before they disappeared.

If you go to the online mirofiche link below, select the model/year and pick the carburetor section from the drop down list you can see where the o-rings go. For example, for my 2006 GS500F it was item number 42 and clearly shows where the o-rings are located.

http://www.hillsboromotorcycles.com/fiche_section_detail.asp

Hope this helps those with this specific problem out.  Seems like it's a common one.

[theUBS]

10 mins is about normal for it to get to temp. Theoretically you're not supposed to take off before that, and worse, do all your tuning in that temp.
However, a lean bike will get hotter than a rich bike, and will there fore misbehave much more till you get it to that temp ... if you tune it in the max temperature situation.
I just jet it to run right and you'll run cooler and reach the steady running state sooner. You are not ever supposed to take off with it cold cos oil may not have gotten everywhere, but 2-3 mins in, it should not be an issue. You're not supposed to stress the motor till it fully comes to temp, and that is that ~10 minute mark.
So, the right jetting will let you start it, 2-3 mins later take off the choke and ride off gently and then have your way with it ~10 mins. 2-3 mins of choke and then take off choke and ride. The right jetting will let you do that as well as not give you any trouble for hot, warm or cold restarts. Hot restarts no choke, the cold = choke, warm may need choke but can take it off in a few seconds. Also at idle the bike should stay just a hair lean. Else hot restarts will be harder. Jet it too rich and hot restarts will be difficult. In fact it may run like crap with it too rich as well. Especially idle. It will easily stall under braking etc etc ...
Cool.
Buddha.

Is there a recommended RPM range to attempt to keep the engine running at during the warm-up?  Fully choked it'll head for 4K pretty quickly, and I usually start backing it off.  Just for my own peace of mind, I'm curious if there's a target number I should have in mind?  Thanks for the post!

[The Buddha]

4k is a good rpm for choke on and warming up. It should hit that in ~30 seconds of startup. Maybe 2 mins of that and you should be able to take it off and it should hold idle - and do so on the coldest day you have in your area). Then you can ride off but make it a low stress ride for the bike - not too high rpm, not too low, dont jump into 6th gear and lug it etc etc, and ~10 mins later it should be fully hot, idle should be no more than a 100 rpm from where it was 10 mins ago, and then you can ride it as hard as you wish.
Cool.
Buddha.

[theUBS]

4k is a good rpm for choke on and warming up. It should hit that in ~30 seconds of startup. Maybe 2 mins of that and you should be able to take it off and it should hold idle - and do so on the coldest day you have in your area). Then you can ride off but make it a low stress ride for the bike - not too high rpm, not too low, dont jump into 6th gear and lug it etc etc, and ~10 mins later it should be fully hot, idle should be no more than a 100 rpm from where it was 10 mins ago, and then you can ride it as hard as you wish.
Cool.
Buddha.

Thanks!  Having never ridden on/in something with an 11K redline before a month or so ago, 4K seems a bit on the high side for just getting warmed up.  If I tried to do the same thing to my car, I think I'd have to take cover.  I've just never seen any definitive rule for warm-up procedure. Cool.

[pjm204]

For me the hanging idle was simply my throttle cable being a little too tight. Because it was such a simple problem it took me awhile to diagnose. I was happy when I figured it out though. I did feel like a bit of a noob.

[The Buddha]

Throttle cable or choke cable being tight sometimes will change with steering turning left or right. Easy diagnosis, and easy fix.
UBS - Yea 4K isn't that high for this bike. Light valves, shims directly under the cams etc etc ... 4K isn't much, in fact lower rpms do more harm, it makes less oil pressure, I would rather rev it than let it run too low revs.
Cool.
Buddha.

[birdman]

I have a stock bike and found a simple solution for the hanging idle.
I checked all cable adjustments and found nothing.
Bike has only 5000 miles on it and I decided to clean the jets on the carbs.  Pilot jet was clogged a bit.

After riding numerous times I realized very small idle screw adjustments made a big difference on how the hanging rpm was acting, so I took a different approach.

I found that if I set the idle below 1000 rpm at around 900 it would not hang, cold or hot.
Problem is that when cold the engine wanted to stall some so I had to use the "choke" to keep it up around 1200 until it was hot.

Solution:  I got the bike hot and adjusted the idle speed to 900 rpm then I turned the mixture screws out by half a turn at a time until the idle was about 1200-1300.  (The mixture screws may be blocked off by plugs if its a virgin, need to drill them out.)
For the last week the weather has been 50s in the AM and 70s in the PM.  The bike idles a little low for the first 5 minutes of my ride to work but once warmed up it is dead on.  I have not had a hangin idle since I did this.

I know the bike is running a little lean since the plugs are ashen white, but considering most of the drive cycle is spent above 3000 rpm I figure just changing the mains would be adequate.

So, yes, at idle you are likely lean.  just enriching the mixture with the screws on each carb with the idle set low will help remove this closed throttle racing rpms.  Make small adjustments and you can dial it in.

[The Buddha]

RPM = oil pressure, cars that spend a lot of time idling, like cabs and cop cars etc etc destroy the cams. You really dont want to set it too much below the 1100 mark.
However you're just suggesting 900 for the start of the experiment and air screw till it hits 1200+. Yea that is the equivalent of basically richening it till it will idle. You could hit 6K and still not idle you know ... Why if the floats are OK it can take 6+ to get idle right, or have the air screw fall off, or it stops having effect really cos its no longer in the gas passage. However a 89-00 GS floats wear high and that makes for a richer and richer bike as it wears. Not correctly rich, but it can alleviate the symptoms of the excessive leanness set from the factory. In a lot of cases, I get carbs that have floats set too high, but it still shows many of the lean signs, it also shows some of the rich signs. Confusing.
Anyway, this procedure can work, or it can not work, or somewhere in between. The right way is ... how they jetted it in canada and england. Look in the manual. to 93-94 in both those countries they sent them with 40/125's.
Cool
Buddha.

[birdman]

Good thought on going too far with the mixture screws. I just checked my setting and they are at 3.75 turns out.

My technical take on this whole issue:

Its obvious the carb airflow dynamics do not match the jets at closed throttle when you are at higher rpm and low load.  Loading the engine (letting out the clutch in gear) reduces the air velocity through the carbs and across the jets and lets the fuel flow drop and match the air better.  With the idle screw set at the correct rpm there is just too much air at that light load.  Not Lean, just too much A/F for the tiny load the engine is creating at closed throttle and 3-4K rpm.
The fact that the idle eventually comes down without loading the engine while its hanging up there is the fact that the jets are bleeding off flow slowly due to this marginal condition. 
Float level may be a small part of the margin.

By closing down the idle screw, as I did, you change the closed throttle airflow across the rpm range so that point where it seems the jets are flowing too much fuel in this little "closed loop" low-load/high flow is now gone.

The reason a richer jet works is that to get the idle at 1200-1300 you have to close off airflow due to the extra fuel now wanting to run the engine faster.  Hence, reducing the closed throttle airflow across the rpm range.
Meaning- Air/Fuel matches the demand of the low load high rpm condition.

I won't get into why all this makes computer controlled fuel injection the superior fuel control under all conditions, rpm, load, airflow etc.

I do agree with the ultimate solution, rejet.  If this marginal condition exists during pilot jet usage then open throttle fuel from the mains is likely shifted too.  My sparkplugs will attest to this.

I wonder how much oxygenated fuel is contributing?  Seems everyone is pumping it year round now.

[The Buddha]

Holeeeeeee cow ... I ahve a headache from reading that ... you speaking extreme Buddha-nese ... like chineese, japaneese and brazilianneese but more confusinger.
Yea OK though.
Cool.
Buddha.

[jt_234]

Newer years have the same problem, but slightly different jet numbers, but same concept. +1 on mains, needles and pilots, and + 1 turn on air screws as well as synch and check on floats.
Now I can rejet for y'all, or sell you the bits to do it, but I'd encourage everyone to do it themselves. At the very least you'd know what's going on underneath your butt. Make sure the shop's you buy from get you the right types of jets, like there is 5-6 types of mains, 5-6 types of pilots, just get the right kind for your bike.
Cool.
Buddha.

OK, so a couple questions along these lines for my 02.  I got the jets taken care of, went one up one each.  I put 20/62.5/130's in it.  Bike runs, haven't road tested it...been raining for days.  First priority.  Idle still jumps around a bit and I still get some backfiring on full throttle and when backing off the throttle quickly.

Thought I had the carbs synched, but am confused after looking at the Clymer manual today.  It shows an 89-00 carb, but shows the float assembly measurements being done with the carbs upside down???  My floats were nearly 1/2" different in height from one another with the carb upside down.  They were close with the carb in the functional position and using the Kerry carb synching method the gas levels were less than 1/8".

The idle screw is only about two turns in and idles at about 1200 but will jump to occasionally and hang for a minute and then return to normal.  I adjusted the air mixture screws and one was about 1/2 turn out and the other two turns out.  I turned them all the way in clockwise and then turned them back out two full turns.  I'm going to turn them out one more turn, is that right?

I tested and replaced most of the O-rings when I cleaned and rejetted the carb.  I'm going to check and adjust the valves next week after I get moved, maybe that will put the finishing touches on the bike? 

[The Buddha]

1/8 th of an inch ... that is like 3-4 mm. Bloody hell, they should be under 1mm off.
2 mm is one jet size. You gotta get them under 1mm off. Top of the bowl and no more.
Then synch is to equate the butterflies, not for floats. The butterflies should be open the same and of course they gotta move together, which they do always.
Then idle screw isn't counted for turns, only air screws are.
You should get these things sorted before going on your test ride, if the theory doesn't work, in real life it definetly wont work. Heck, I have seen well setup bikes have all sorts of trouble in real life.
Cool.
Buddha.

[drummer89s]

Ive been having a problem with the rpms hanging around 4k when the engine is revved while warmed up.  Then the rpms dop back down to a normal idle after a few seconds. I have recently pulled the carbs and cleaned them, and its doing the same problem.

wondering if anyone else has input on this?