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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: k75novice on August 09, 2017, 09:36:31 AM

Title: Throttle not returning fully closed. Anyone had this issue?
Post by: k75novice on August 09, 2017, 09:36:31 AM

I just replaced the upper TB boots in another effort to solve my high idle issue. Afterwards, the bike ran as before, and I noticed while adjusting the idle and syncing the TBs that the throttle won't return closed; the idle adjustment screw doesn't hit its perch unless I physically push it down. If I let go, it returns to opened about 3-4mm.


Has anyone else had this issue? Am I lucky in that it may be a matter of cleaning the springs? Or might some PO have messed with these; do I have to take the intake plenum and TBs off to rewind the springs tighter? I'd like to avoid taking the intake plenum off as it was really annoying last time.


Bike is a 1994 K75 ABS


Thanks,
K75N

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: Motorhobo on August 09, 2017, 09:55:20 AM

I have the same issue, have had it for a while. I was able to get the idle down some with a throttle sync adjustment but I still idle a bit high and somewhat uneven. I have been meaning to deal with it but...haven't gotten around to it yet. So, yeah --- I could use some guidance here as well.

I also tried to adjust it out on the choke cable...without much success. I think my problem is related to the fact that I took the throttle bodies apart to clean them last time I had them off and had a helluva time getting them back together and probably screwed something up. So -- a word of advice to anyone reading this -- don't do that.

There's also supposed to be an adjustment screw at the handlebar end, but I didn't have much luck with that either. I've read that the cable routing can be an issue as well since it'd pretty cramped back there behind the airbox....

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: Filmcamera on August 09, 2017, 10:35:34 AM

I had my throttle bodies off at the weekend and the only thing that occurs to me is that I found a pretty well hidden adjusting screw underneath the throttle bodies, on the underside opposite the regular throttle return spring adjuster.

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Maybe that is screwed in too far not allowing the spring to fully return?

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: Inge K. on August 09, 2017, 10:58:01 AM

Quote from: Filmcamera on August 09, 2017, 10:35:34 AM

I found a pretty well hidden adjusting screw underneath the throttle bodies,

4V models only
.
.
Check that the clamps døn't interfere With the thottle mechanism, and that the throttle switch is
correct adjusted.

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: The Mighty Gryphon on August 09, 2017, 12:46:39 PM

Have you checked the engagement of the gears in the throttle assembly on the handlebar?  There are two marks that need to be aligned for proper throttle action.

The throttle cable is also sensitive to routing and it needs to be free to move along it's entire length.  Pinches or clamping will cause problems.

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: Laitch on August 09, 2017, 12:57:18 PM

Quote from: Inge K. on August 09, 2017, 10:58:01 AM

Check that the clamps døn't interfere With the thottle mechanism, and that the throttle switch is
correct adjusted.

Here is an illustration from the K100 manual on the site. Several members have cured throttle response problems by adjusting this clamp correctly.

Pay attention to the position of this clamp..jpg (23.53 kB . 768x254 - viewed 1138 times)

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: rbm on August 09, 2017, 06:28:39 PM

Looking from above with the TBs removed (shown is a K75 motor, K100 repeats the middle intake clamp position):


(https://lh3.googleusercontent.com/Vn853DbYVaOZ2pduERBsH0kjKnWwWb0xuucU_6jZyk5OW0P2QLJ9KJg8uxJtzALlXq87C8diQs7A-QrYduFPN9aO77MzW0CI_UYWEWnw1ZgUAeZ-ZYbF_Wdbwq-qHvt34-sevpnqRBZhQbwNW7WKxCSvxpANTxqdhz-GwrzJFmKnSJsiQVZMceKfDdnb54zOAdjNG4DsFTwmALvmsLzgtxndva-CF0WzcaiO_xouSbYhuCFf-QWi-9XauPJQyI-UzZ-u-i9fl10tUjs0ruPBVVv2K5RcLxnfK5sO3CI3eOuYGdvV_DkPgiFqv-agamxp80PO8hP6-6z0-FAsLzpgXGZXwWzCUt2olFZ1trEa-jHflO4abCm_ragYzqnSwjyuXFIti3DFmlwj-xn5xGSO9PynD0GVi9QHap7wosZ_kqq8wXvPF9DvZQ3NHLshpHpT9vLwr2Xh9EkDnr-FbPNKXNKVhPwIVikBjCTiB8_ZP7NFisCbTu6bgfsGMPrm-reb4dtsHXLamhkjqeu1mDkKU-Iu7fEchhJ2hfnuMkyftpYmhExXhwMPy6Sk48ipauYIpaLFB85LDAZAFIHgQ7JUBRRzLZpkvqD-fFyVmnsRvKnp7kffa1cO70iZ=w1982-h1486-no)

Title: Re: Throttle not returning fully closed. Anyone had this issue?
Post by: Beardlife on September 24, 2017, 06:11:08 PM

I just cleaned my throttle bodies, and had this problem. I traced it to poorly balanced throttle bodies, the spring linkage between bodies was holding the throttle open.

 I fixed it by first setting the throttle blades as close as possible using a micrometer and measuring in the bore from the top lip, then following this procedure, with one exception:
http://www.k100-forum.com/t1526-how-to-balance-the-throttle-bodies-solved

I don't see much of a point in using an idle bypass screw if the throttle bodies are clean and balanced, so my idle bypass screws were used as little as possible.