Throttle cable needs adjustment?

[mikeo996]

Guys, hoping that you can tell me that I'm on the right lines.

My throttle cable snapped at the Throckmorton handling day a few weeks back, but (with the help of friendly club members) I managed to fit a new one, which luckily I was carrying. I noticed right away that it had a bit more of a tendency to kangaroo on light throttle, but not too badly.

Since then I've taken it out on a spirited country lane drive, where I didn't notice any significant issue (but probably used little light throttle), but today, taking it out to fill up with petrol it was a nightmare in traffic. It idles fine, and is fine under acceleration, but is horrible at steady, low speed.

The guy who helped me at Throckmorton (thanks again Nigel) said, I think they they do tend to stretch a bit initially, and that there may have been a bit of slack to take out. Does this sound right to the collective and if so what's the fix, just a twist of the screw fitting at the roller barrels end (it's a k-series R300 on roller barrels) or something at the pedal box end?

I've taken the pedal box cover off and the cable does feel slightly slack now at that end, but I'm not sure why, if you have pressure on the throttle pedal, any slack should matter.

Before I pull it out and put a couple twists on it, as I say, just want to make sure I'm not barking up the wrong tree.

Thanks,

Mike

[Jonathan Kay]

Has the pedal height changed?

Jonathan

[mikeo996]

Good question, which I'm struggling to answer, so I suspect not by much. When I first got in it after the change I thought it had moved a bit (downwards?) but it's still okay for heel and toe, so not by much, and I'm not trusting my recall. And onviously I have adjusted to it now if there was a change. 

[Jonathan Kay]

I have an unproved suspicion that some kangarooing in some 7s is sometimes caused by underdamping of the whole of the control loop including the human bits as well as the pedal, cable, throttle springs, airflow lag etc. Does it decrease if you add some friction by leaning your leg against the cockpit?

Jonathan

[martyn]

Sounds like you need to add a little bit of cable tension.  Shouldn't need to remove anything, just rotate the plastic adjuster a few turns.

You want enough tension so the pedal is held positively against the upper stop (the pedal will swing freely when slack is present).  But not so much tension that the revs dont drop cleanly back to idle after a blip.

Personally, I like as much cable tension as I can get away with.  As Jonathan says above, this adds damping/resistance to the whole system.

[mikeo996]

You mean presumably the black square bit of plastic that clips the cable just below the roller barrels? Feel a bit of an idiot because I was planning to remove the cable and twist that rather than twisting the holder..duh!

I'm sure you're right about the bracing Jonathan, but doesn't apply here as it's a sudden change. I have found that, once started,  the only way of managing a kangaroo is getting right out of the throttle and starting again rather than any modulation.

ETA Having checked the assembly guide now I can see it is the black square bit I need to adjust, will give it a go later.

[martyn]

Yep, the black square bit. It unclips from its mounting, can then be screwed in or out and then clipped back in.  By doing this you're actually adjusting the length of the housing that the cable runs through and therefore adding or removing tension from it.

Unclipping it can be a bit awkward, and it may help to get a third pair of hands to rotate the throttle linkage open a bit to give you a bit of cable slack to work with.

[nigelpugh]

Mike,

as I said when I helped to fit it at Throkmorton, they need to settle in, then adjust them to suit both you and your car.

as I recall we fitted the new cable with too much slack in the take up when we were at the event, so it would need to be adjusted to take the slack out.

just as a did when fitting your new cable, pop the black plastic ferrule mount out, and adjust to make the outer cable longer, which will reduce the take up slack.

of course all of this normally changes the pedal height too, but you can adjust that by increasing or reducing the slack as mentioned.

also if you get to a good compromise of cable slack, but not a pedal height that you are happy with, then just adjust the throttle pedal by bending the assembly to make the position as you want.

hope that is as clear as I can make it?

nigel.

[mikeo996]

Thanks Nigel (sorry, I haven't checked back here the last couple days). I'll hopefully be able to have a fiddle with it next week.