Idle speed adjustment screw not seated!!??

[dom_ada]

Hi everyone.  I am at the end of my 89 k100 rt (lt conversion) now cafe racer style build and I am ironing out the last of the niggles.

I hope I am not duplicating a thread but I can seem to find info on this problem:

When resting at idle the idle adjustment screw (and throttle bodies) sits 1mm approx off where it should seat; hence it idles a little too high and there is no way of adjusting it down as the gap between the adjustment screw and where it should seat just increases. This is odd right? It is as if the throttle cable is holding it open slightly (this is definitely not the case.. all cables have adequate free-play.)  It is possible to push lightly down on the screw and it seats and the bike then idles at the correctly adjusted position. But as soon as the throttle is blipped the gap reappears. I just don't understand what is holding it up.

There are the four other adjustment screws... with funny blue paint on them... I tried turning them all in random directions and now... haha, not really.. I so nearly did as i'm sure they would resolve this if all were proportionally adjusted.  But thank god I read up on it first as this would potentially completely ruin the intake balance right?

Any ideas of what on earth is going on would be greatly appreciated.
I am just waiting for a seat I built to return from the upholsterers and then I'll stick up some lovely pictures. :2thumbup:

[Inge K.]

Could be that the TPS at the rear end of the TB bridge is wrong adjusted.

[tg4360]

Did you happen to replace the throttle and master cylinder?

The K1100 bits use a lightly different cable perch. 

[dom_ada]

Ah ha. I did.. and did. Common issue then? I've used a Venhil throttle.

I'm just researching the TBS..? Is that the last adjustment screw? I couldn't see what it did.. looking it up now.
Thanks folks.

[dom_ada]

Adjusting the tps will not allow the whole body to rotate down/towards.. which is what I think needs to happen.

[Inge K.]

The TPS is a couple of switches inside a black housing in the rear end of the TB bridge.

It's one screw on each side of the black housing, loosen these to screws before you adjust it by
turning the housing c.w. or c.c.w.....correctly adjusted you should hear a click just when opening
the throttle.

If the TPS is turned to much c.w. (wiewed from behind) it can hold the throttle a tiny bit open.
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If this doesn't help, check the choke mechanism in the same area....this isn't actually a choke.....
it just opens the throttle a tiny bit.

[tg4360]

Here's the scoop on the K1100 throttle cable on a K100 perch.  You have to cut about three or for mm off the cable perch where the cable goes trough to allow the free end to be long enough to let the butterflies close to the stop.

Here's the write up I found that helped me when I put a K1100 master cylinder on my K100GS conversion:

http://www.k100-forum.com/t1223-installing-k1100-front-brakes-on-a-non-abs-k100rt

It seems you might just not have enough free cable in which case even if it's not the 1100 setup, you can probably still make the mods needed to make it work.

The other possibility is that the "Choke" cable (really just two stage fast idle) is not adjusted correctly or is hung up somewhere and it holding the throtlle plates open just like it's supposed to even with the lever "closed".

TG

[dom_ada]

The TPS is a couple of switches inside a black housing in the rear end of the TB bridge.

It's one screw on each side of the black housing, loosen these to screws before you adjust it by
turning the housing c.w. or c.c.w.....correctly adjusted you should hear a click just when opening
the throttle.

If the TPS is turned to much c.w. (wiewed from behind) it can hold the throttle a tiny bit open.
------------------------------------------------------------------------------------------------------------------------

If this doesn't help, check the choke mechanism in the same area....this isn't actually a choke.....
it just opens the throttle a tiny bit.

Awesome! I had a look through a haynes manual too and you must be right. The only mystery is how this happened without me touching it...(I don't think I touched it) I'm sure I didn't have this issue before I began and the bike idled a perfect rpm.

I removed the throttle cable (gap was still there.) Will try removing the choke cable too before touching the tps (though I wound it to a very slack position so I don't think that's the issue.)


Regarding the cable perch.  I made my own cables (throttle and choke) to length. Will investigate further anyhow.
Many thanks.

[dom_ada]

Here's the scoop on the K1100 throttle cable on a K100 perch.  You have to cut about three or for mm off the cable perch where the cable goes trough to allow the free end to be long enough to let the butterflies close to the stop.

Here's the write up I found that helped me when I put a K1100 master cylinder on my K100GS conversion:

http://www.k100-forum.com/t1223-installing-k1100-front-brakes-on-a-non-abs-k100rt

It seems you might just not have enough free cable in which case even if it's not the 1100 setup, you can probably still make the mods needed to make it work.

The other possibility is that the "Choke" cable (really just two stage fast idle) is not adjusted correctly or is hung up somewhere and it holding the throtlle plates open just like it's supposed to even with the lever "closed".

TG

Ah, I'm with you now. Could be :yes Thanks

[Inge K.]

About the choke cable......by removing/undoing  the cable....this won't make any differnce if the problem
is at the mechanism down at the TB's
(which it probably is, if the choke is the reason to your problem and the cable has the correct length).

Between TB 3 & 4 you see a cam plate and a roller, it should be a opening between these two when the choke is off.

[rbm]

One mistake I make when I do the TPS adjustment is to press downwards on the TPS body as I tighten the screws.  This is wrong and can introduce friction that keeps the throttle butterflies slightly open.   I don't know if others have the same problem as I, but when positioning the TPS, make sure that it remains centered on the shaft.  When the TPS is loose, you can just feel the slight amount of slop necessary to maintain.

Below is a picture of the high idle cam on the K100/K1100 throttle bodies.

You can just see the gap between the roller and the cam.
This is a picture with the fast idle fully engaged by the choke lever.

[tg4360]

Let us know what it ends up being....


And pictures! We want to see your bike!

[dom_ada]

:euro

I've got some time in the morning (uk) so i'll examine the three possibilities. Choke/cable/mechanism binding or something, Tps wrongly adjusted or the unlikely but possible chance that i've missed the throttle cable/body fouling something... no, surely can't be that  :dunno2:

Here is a taster of the bike. You can see the front un-upholstered seat. Should be back with me late next week and then i'll do a little write up.

[dom_ada]

After all that it turned out to be the choke cable tension (I didn't previously know that the choke lever directly affects the tb arm).  I thought it was slack and as winding the adjustment didn't seem to affect the height of the tb arm.
I wound it all the way in and the gap was gone.. to the point now where the idle speed is a fraction low and I have adjustment in the idle speed screw to bring it back up again.

So after all this it turned out to be one of the simplest things.
Thanks very much for all the input everyone.  I have a much greater understanding of this section of the bike (which I didn't plan on delving into until next winter when I remove it and give it all a good clean up.)

Thanks again.

[Inge K.]

Nice that you get it sorted.