Author Topic: Idle wont come down  (Read 2119 times)

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Offline Gorms

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Idle wont come down
« on: September 09, 2009, 05:12:11 PM »
cb550k

It idles fine on startup but when I rev it, it doesnt want to come back down until I twist the throttle past its stopping point (using the "push" throttle cable I guess).  The rod across the carb bank that opens the slides and moves when the throttle it opened fully returns to its idle position and closes against the idle screw but the idle stays up until I twist the thottle back.  The wheel that the cables connect to spins backward a bit when I twist it back but the rod doesnt move.  It works though.  I tried tightening the push cable to have it do this by itself but that just makes the thottle bind and it wont return at all.

Does this make snese?  Hopefully I did alright explaining it.  Any ideas?

BTW the carbs were completely rebuilt so I highly doubt the slides are gummed and sticking open.



Offline DukieDukenDuke

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Re: Idle wont come down
« Reply #1 on: September 09, 2009, 05:49:36 PM »
Run a search for "high idle", there are lots of relevant posts on this subject.
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Offline Spanner 1

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Re: Idle wont come down
« Reply #2 on: September 09, 2009, 09:51:26 PM »
Carbs need to be sync'ed....do a search for carb sync......



Offline the technological J

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Re: Idle wont come down
« Reply #3 on: September 09, 2009, 10:00:55 PM »
you probably need new throttle cables if they are binding up on u or a good cleaning  and lubing of all those pivot points... especially at the spring.... i would disconnect the cables(both ends) and see how much tension it takes to move them.... and snap the "wheel" check the spring and how it works.. if it snaps back you"ll know it the cables ... if u havent bought any cables and and u think the originals are on it go head and buy some but some cable lube might work for now



Offline Gorms

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Re: Idle wont come down
« Reply #4 on: September 09, 2009, 11:15:38 PM »
Carbs have been rebuilt and all cables are brand new and are not binding.  The throttle returns to its idle position promptly and smoothly but the idle stays high unless I twist the throttle backwards a few degrees.  This rotates the wheel on the carbs slightly but that wheel does not turn the carb slides at all as there seems to be some play in the wheel when twisting backwards.

Maybe I do need to sync them but the idle is fine when I "backtwist" the throttle.  Doesnt seem like this is a sync issue to me?



Online Johnie

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Re: Idle wont come down
« Reply #5 on: September 10, 2009, 07:39:24 AM »
Are you sure your return spring is not loosing strength. Last, if the slides are set to high they could cause the problem. A sync to turn them down a bit would help to lower the idle. Just one slide up to high could make that idle fast.
John
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Offline tomsweb1

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Re: Idle wont come down
« Reply #6 on: September 10, 2009, 07:48:10 AM »
That's not a sync problem. My carbs are perfectly synced, and I have the same problem. I'll let you know if I find out why. Do you have any freeplay in the throttle. I don't, but I have it adjusted all the way, no room to get more.
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Offline Bill/BentON Racing

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Re: Idle wont come down
« Reply #7 on: September 10, 2009, 07:54:00 AM »
Your carbs can be perfectly synced and if they were synced too high,slide can't physically go down,resync lowering slides,can check by looking or turning idle screw off of stop.Bill
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Offline MCRider

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Re: Idle wont come down
« Reply #8 on: September 10, 2009, 07:56:05 AM »
That's not a sync problem. My carbs are perfectly synced, and I have the same problem. I'll let you know if I find out why. Do you have any freeplay in the throttle. I don't, but I have it adjusted all the way, no room to get more.

If you've got the adjuster at its shortest adjustment, and there is no freeplay in the throttle, you have a problem. (duh)  Disconnect the A cable altogether and see if it returns to idle.

Looking elsewhere, with no freeplay in the throttle is likely wasting time. There may be another problem, but with no freeplay you can't do valid diagnosis.
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Offline MCRider

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Re: Idle wont come down
« Reply #9 on: September 10, 2009, 07:56:29 AM »
Your carbs can be perfectly synced and if they were synced too high,slide can't physically go down,resync lowering slides,can check by looking or turning idle screw off of stop.Bill

Yes, what he said.
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Offline Gorms

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Re: Idle wont come down
« Reply #10 on: September 10, 2009, 07:57:09 AM »
The only freeplay I can find is in the wheel on the carbs which the cables connect to.  It only has play in the counter-rotating direction.  I tried to tighten the push cable so that the freeplay slack gets taken up when I release the throttle, but this causes some binding (in the cables I think) and the throttle wont return.  Maybe my solution is to keep this tight, but get a stouter return srping and lube my cables.  How and with what lube does one lube their cables?  I could probably search for that...I'll do that now...



Offline GoatBaSS

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Re: Idle wont come down
« Reply #11 on: September 10, 2009, 07:59:23 AM »
Pay attention to routing and make sure the cables are not to long or to short. It seems you have the movement there, but the carb connections are inhibited in the full play with out the proper persuasion. Also check to see that the throttle housing on the bars is right. Could be a little off.....
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Offline Spanner 1

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Re: Idle wont come down
« Reply #12 on: September 10, 2009, 08:23:26 AM »
Guys, he says he gets idle when he pushes the throttle bar down beyond the range of the idle screw, meaning slide(s) are too high, even at min. idle setting = carb sync.



Offline Gorms

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Re: Idle wont come down
« Reply #13 on: September 10, 2009, 08:34:23 AM »
But only the wheel rotates and not the slide rod...aka there is freeplay between the wheel and the slide rod.  Maybe its moving imperceptibly.  I will look into getting a sync tool.



Offline MCRider

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Re: Idle wont come down
« Reply #14 on: September 10, 2009, 08:59:34 AM »
The only freeplay I can find is in the wheel on the carbs which the cables connect to.  It only has play in the counter-rotating direction.  I tried to tighten the push cable so that the freeplay slack gets taken up when I release the throttle, but this causes some binding (in the cables I think) and the throttle wont return.  Maybe my solution is to keep this tight, but get a stouter return srping and lube my cables.  How and with what lube does one lube their cables?  I could probably search for that...I'll do that now...

The point to remember is that everything should work fine with just the A cable. The B cable is immaterial and is just along for the ride. It should have no effect on maintaining or achieving idle. It can be removed without consequence.

In fact you may want to remove it while diagnosing this problem so it doesn't interfere and lead you astray.

I vote for your slides, even though synched, are too high to start with.
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Offline tomsweb1

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Re: Idle wont come down
« Reply #15 on: September 10, 2009, 04:40:43 PM »
... then what the crap is the point of the B cable??
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Online Johnie

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Re: Idle wont come down
« Reply #16 on: September 10, 2009, 04:49:11 PM »
... then what the crap is the point of the B cable??
Cable B is so that if cable A breaks then cable B can bring the throttle back down.  Safety feature...
John
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Offline shizzomynizzo

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Re: Idle wont come down
« Reply #17 on: September 10, 2009, 04:51:27 PM »
Your carbs can be perfectly synced and if they were synced too high,slide can't physically go down,resync lowering slides,can check by looking or turning idle screw off of stop.Bill

Spot on, i was trying to say it earlier, but couldn't put it together so concisely.

I started with a bench synch with a 1/4 drill bit, and this was too high. i had to lower the slides (a lot) about 2 whole turns to get them down enough to stop this problem.
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Online Johnie

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Re: Idle wont come down
« Reply #18 on: September 10, 2009, 05:11:38 PM »
Your carbs can be perfectly synced and if they were synced too high,slide can't physically go down,resync lowering slides,can check by looking or turning idle screw off of stop.Bill

Spot on, i was trying to say it earlier, but couldn't put it together so concisely.

I started with a bench synch with a 1/4 drill bit, and this was too high. i had to lower the slides (a lot) about 2 whole turns to get them down enough to stop this problem.
Good point...I know our very own dashing TT likes to use the flashlight approach. He opens each slide just until the light starts to appear. I agree the drill bit is to large.
John
1969 CB750K0 - Candy Blue Green (current)
1970 CB750K0 - Candy Ruby Red
1970 CB750K1 - Candy Gold
1973 CB750K3 - Candy Bacchus Olive
1974 CB750K4 - Flake Sunrise Orange
2000 1500 SE Wing


Honda's owned in the past:
1965 65SS, 1969 CB350, 1971 CB350, 1972 CL175, 1974 CB450, 1975 CB360T, 1977 CB750K, 1980 CM400E, 1981 CM400C
Oshkosh, WI  USA



MotoMartin

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Re: Idle wont come down
« Reply #19 on: September 10, 2009, 05:14:21 PM »
How quickly do the revs come down when you push/force the throttle stop closed? If they come down quickly in response, it could be that the slides need a resync. However if the revs stay high and slowly come down it seems more likely that you have an air leak (even more likely as it sounds like the carbs have just been off for a cleaning.) With the motor running try squirting starting fluid (or carb cleaner) around the intake manifolds and see if there is a change in rpms.
I have similar problems with my bike...



Offline MCRider

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Re: Idle wont come down
« Reply #20 on: September 10, 2009, 05:44:04 PM »
... then what the crap is the point of the B cable??
Cable B is so that if cable A breaks then cable B can bring the throttle back down.  Safety feature...
Yup, and that's all. (which could be a lot I guess) but it does not contribute to, nor should it be made a part of, the bike's ability to idle.
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Offline tomsweb1

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Re: Idle wont come down
« Reply #21 on: September 10, 2009, 05:53:16 PM »
Neat. Ok. Now here's my thing. I don't know about your bike there, gorms, but my #2 is not adjustable as far as syncing goes. This means the other three are synced off that one. Therefore, the only thing our little idle screw does is change the engine speed when the throttle is in the neutral position. Our problem is our throttles are not achieving neutral position. Why is the question.
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Offline Gorms

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Re: Idle wont come down
« Reply #22 on: September 10, 2009, 06:40:48 PM »
Ya tom.  I did some poking and proding today and it now looks like the stop that hits the idle screw doesnt close all the way...only when I twist the throttle back.  I got a new, stronger spring and still wont clost by itself (or at least wont close enough for a low idle).  I even cut some loops off the spring and stretched it further.  Still wont close.  I either need a super powerful spring or there is something wrong.  I want to check the pull cable and make sure its not too tight (that just occured to me).



MotoMartin

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Re: Idle wont come down
« Reply #23 on: September 10, 2009, 06:42:12 PM »
Quote
Cable B is so that if cable A breaks then cable B can bring the throttle back down.  Safety feature...
Does n't the throttle return spring do that?
Our problem is our throttles are not achieving neutral position. Why is the question.
In his first post he says the bike idles good then when it is reved they stay high. Could this be a choke issue?
I would definately try taking all the tension out of the throttle cables, let it idle with the cables real loose to see if that makes any difference.



Offline Gorms

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Re: Idle wont come down
« Reply #24 on: September 10, 2009, 06:44:59 PM »

I would definately try taking all the tension out of the throttle cables, let it idle with the cables real loose to see if that makes any difference.

Thats an excellent idea and I will do that next.  Come to think of it I dont remember having the issue before the cables where installed.

 

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