Engine revs

[stuart147]

Looking for some help here with a problem that is very sporadic and hard to pin point the conditions at the times it occurs.

When lifting off the accelerator to come to a stop, very occasionally, the revs seem to take ages to reach the tickover speed of about 850rpm. Yesterday, in the heat and the fan being on, the revs would not settle to tickover at all instead staying at about 2400rpm. This obviously kept the fan on which made the original problem worse. I pulled over and done the 5 times pedal press and all was O.K.

Why would this happen only occasionally? Why do the revs seem to take ages to settle?

K Series EU3 by the way.

Stuart

[Jonathan Kay]

I'm sure there are other causes, but start with checking for stiction in the pedal, the cable and the throttle. It might be easier to disconnect the cable ends to enable you to play with each separately and help localise it.

There's a known problem with the throttle sticking due to overtightening of something or other.

Recent discussion.

Jonathan

[DJ.]

I think I would start with checking/changing the throttle cable. I had this years ago on another car and was convinced it was the idle control valve. I only found the real cause when the cable snapped driving home from work

[SM25T]

If plastic plenum .... overtightening air filter jubilee clamp can stop butterfly returning to rest. As above .... sticky throttle pedal pivot or frayed inner cable ?

[martyn]

I can simulate the symptoms you describe on mine by having the throttle cable tension too high. I'm not suggesting this is the case for you (unless you've been fiddling with the tension recently), but all signs point to the throttle cable.

[stuart147]

Thanks for the quick replies. I will take off the cable and have a look at the inner and also the pedal pivot. The cable is the original one so may just as well change it to be on the safe side. A call to Redline tomorrow.

The throttle body on mine is alloy so over tightening of the air filter would have been the easier fix.

Is the cable relatively easy to change?

Stuart

[Jonathan Kay]

Is the cable relatively easy to change?

Even for me! :-)

Jonathan

[SM25T]

Don't need an expensive complete cable Stuart. Visit your local bike shop and buy an inner cable with a fixed barrel nipple one end. Buy a screw nipple on line for pennies. Barrel nipple at engine end .... check required diameter to fit in your quadrant. Screw nipple .... or electrical screw connector is fine ... behind the top of the throttle pedal. Cut excess cable off. Inner cable will cost less than £3. Buy two and keep one as spare. If you remove your inner cable before shopping .... get the cycle shop to cut to length with their triangular jaw wire cutters ... stops end fraying like it does if you use sidecutters or a hacksaw.

[SM25T]

The beauty of the cycle inner cable is ... it will be a stainless cable ... with a PTFE or Teflon coating ... easy running.

[Stridey]

Just done throttle cable on mine (xflow). Easy peasy, and cheap (£8.50 from Redline).

Yours may be different, but I had to undo the pedal box cover to get great access to pedals from above. 

My sticky throttle occurred after a very hot run, gunk gets into the cable and eventually seems to grease up. Over time it just didn't return to idle quickly and could feel like I had cruise control... Had to hook my foot under the throttle a couple of times to release it... Not good.

Ive rescued the old cable by poking the cable from an emergency throttle pack that's sold in a tin, clearing the gunk out of the tube and then replacing the cable through a bit of 3in1 oil. I'll add it to my touring pack of spares....

its  an easy job and satisfying to know you could do it quickly if it snapped, or failed in future.

[stuart147]

Again, thanks for the replies. It looks an easy job as I have already got the old one off. I happen to have new cycle cable in the garage as my son is a keen cyclist. He will not notice one missing. 

Stuart

[stuart147]

Help again. Could someone post a photo of how the throttle cable attaches to the pedal. I think I know how it should go, but looking for confirmation. 

Stuart

[Stridey]

On mine the fixed nipple end of the wire goes in the centre hollow of the pedal tube. To get the old cable out and new one in I had to bend the 'ears' of the tube back to slot it in, then close it up with strong pliers.

i have seen this method: http://caterham420r.blogspot.co.uk/2016/01/build-day-35-throttle-cable-brake-and.html.  Which looks interesting and perhaps easier/quicker if doing a rolling repair. 

[Jonathan Kay]

While you're waiting for the photo here's what the Assembly Guide says:

THROTTLE CABLE FITMENT

71 Attach the throttle cable to the linkage on the throttle body by engaging the nipple in the throttle operating lever and then clipping its square shaped black plastic adjuster onto the adjacent bracket. This adjuster can be threaded up and down the cable outer to adjust the throttle pedal position.

72 Pass the other end of the throttle cable through the 22 mm hole in the front of the pedal box and clip the plastic seat into place. The inner cable is fed into the slot on the top of the pedal with the portion of cable protruding past the cable termination located through the hole. The top of the pedal should be gently squeezed with a pair of pliers to capture the cable and prevent it escaping.

NOTE

In order to obtain a preferred pedal height and achieve adequate cable tension it may be necessary to bend the top of the pedal prior to locating the cable. This is done by inserting a Phillips screwdriver into the top of the pedal, bracing the bottom of the pedal with a block of wood, and gently bending the top of the pedal so as to take up the slack in the cable. Finally use the adjusting mechanism at the throttle body end of the cable to remove any free play. 

Jonathan

[stuart147]

Thanks for the quick replies. I am going with Stridey's method.

Stuart