Topic: EDIT: Fresh start - Hanging Throttle

[Nortstudio]

1976 550K with 087a carbs:

I am starting a fresh thread - because I have probably driven all of you batty with the last one.  I am having a real hard time with these carbs after a fresh rebuild. 

I'm getting hanging idle - even after new throttle cables.  The weird thing is that it seemed to help when I first put them on.  Now, after riding a bit, it's back to cruise control hang mode.  I checked the throttle butterfly with no cables on there - and it snaps back quick.  When i first put the new cables on, seemed good.  Took it for a ride, and it gets worse.

Is there a possibility that when gas starts to flow through the carbs while running that it makes the throttle stick???  That's the best I can come up with.

Thanks in advance for putting up with my constant questions....

[Rookster]

Long shot - Are you running a fiberglass tank?  The E10 gas can delaminate fiberglass tanks which turns into a sticky paste like substance once the gas evaporates.  If so there is really no permanent fix other than lining the tank which is a band aid solution.  There is no ethanol free gas available to the general public in the U.S. anymore that is easily acessible.

My opinion on hanging idles is that most are the product of an air leak.  Think about it, how can the engine rev unless there is fuel or air (or both) being fed into the the combustion chamber?  Try wrapping some shop rags around your intake boots and soaking them with either gas or wd40 after the motor is running.  When you spray it all over the boots it runs off pretty quickly.  You need a way to allow the engine to suck gas/wd40 through the leak.  My bet is that your intake boots are leaking air.

Scott

[Nortstudio]

Sorry, I should have been more clear.  The link arms are actually hanging in the air, instead of snapping back.  So no air leak (or not the major problem - may have that too, who knows at this point).

The weird thing is that it doesn't do it in the beginning - which might go toward your theory of the tank/gas providing something weird.  I cleaned the tank with The Works, and then did the whole routine to clear it out... thoroughly.  I have gone through a bit of gas at this point, so i hoped any residue i couldn't get out would have been passed through the system by now.

Here is where it's at:

The butterfly snaps back quick when there are no cables attached.

The throttle cables have been replaced (and it seemed to help) and lubed.

When I first put the new cable on, it seemed great, but then I rode it for a bit, and the hanging started again.  I got off, and looked at the link arms, and they are staying in the air.

[Nortstudio]

To confirm my kooky fears about gas playing a roll in all this, I just checked the throttle action, after the bike has been sitting for a couple hours.

No hang that I could tell without the bike running.....

I'm tempted to take a ride to see if it gets effected again, but night riding in Brooklyn traffic with a hanging throttle could be...well, not good!

[Tews19]

Sorry, I should have been more clear.  The link arms are actually hanging in the air, instead of snapping back.  So no air leak (or not the major problem - may have that too, who knows at this point).

The weird thing is that it doesn't do it in the beginning - which might go toward your theory of the tank/gas providing something weird.  I cleaned the tank with The Works, and then did the whole routine to clear it out... thoroughly.  I have gone through a bit of gas at this point, so i hoped any residue i couldn't get out would have been passed through the system by now.

Here is where it's at:

The butterfly snaps back quick when there are no cables attached.

The throttle cables have been replaced (and it seemed to help) and lubed.

When I first put the new cable on, it seemed great, but then I rode it for a bit, and the hanging started again.  I got off, and looked at the link arms, and they are staying in the air.

This is a 550k 78' right?

From your description sounds a lot like mine.. Minus the either hanging idle/high idle to just dying at idle.. When you drive it and come to a sudden stop does it putter and feel like it wants to die???

[Nortstudio]

Thanks for pointing that out. It's a 1976 550K.

This is more of a physical thing, with the link arm actually hanging in the air too long.

[bollingball]

Can you try a stronger return spring?

[phil71]

stronger return springs are more a band-aid than an actual cure.
I'd be checking the cable routing, also try it with the bars swept across from lock to lock.. could be too tight and the slightest movement of the bars takes out the free play. Also, I can't remember if that's push-pull, but you might wanna look at the 'push' tension. It served a few purposes, one was to give you the ability to spin the throttle a little forward to make neutral a little easier to engage at a light when hot. Is there a spring-loaded thumbwheel between the 2 cables leaving the throttle assy?

[KingCustomCycles.com]

Just a theory............while riding the incoming fuel and air are cooling the carb parts in the venturi area and causing the slides to bind.  This isn't normal, but is possible if the clearances are too tight on one or more.  You have described this as a physical binding which will be something changing in the carbs enviroment, vibration, angle, temperature, etc.  Troubleshooting 101, what changes, and why, and how does that fit the symptoms? 

[Nortstudio]

Thanks guys.  I'm hoping it's the cables.  I am going to try to reroute them today, but cable theory seems less likely to happen when the bike warms up.  Granted, they could move while riding.

Phil, you lost me at the end there.  I do have the push/pull, and it does have that little extra forward motion at the end, but I'm not sure which thumbwheel you are talking about.

King, I am trying to narrow down the symptoms, and when the occur.  So far it's been tough.  At this point I know:

the spring snaps back with no cables attached.

When cables first attached, seems to snap fine.

Rode the bike, and snap back seemed fine (I tested letting go of the throttle while riding).

After a short ride, it began to bind.  Acted just like a cruise control.  Let go of the throttle and it doesn't snap back.  Saw this happen with both the throttle lever, and the link arms.

[Scott S]

 Have you sourced GENUINE Keihin slow jets yet. I'm telling you...I went through the same, exact thing. I even have a long thread about it on here somewhere...

[Nortstudio]

Scott, thanks for your input.  While I do feel I need to get those slow jets, at this point I'm pretty sure the hang is not caused by a jet. I am physically SEEING the link arms hang in the air longer than they should.

I also haven't been told a good source to buy them. A place I could be assured has the proper size jet. At this point, o have 2 sets of the wrong ones, so I don't need more

This is what i have planned to do today:

1. Reroute and secure differently the throttle lines.  Se if that makes a difference.

2.  Swap the throttle itself, to see if this new one that is on there is getting caught on the switch housing.

3. Remove the carbs, and see if there is anything obvious inside the bore that is getting hung up.