15 replies to this topic

[jakejakejake1]

Hi Everyone,

I have had this problem happen four times now, luckily I have managed to avoid disaster (up until now anyway).
The basic problem is, the throttle jams fully open sometimes, its always happened after driving along the motorway, then when I come off the motorway and start driving 'spiritedly' along the A-roads, I have managed to notice symptoms that occur before it fully jams which have helped avoid any dangerous incidents but obviously this is still not an ideal situation.

1. So far has happened when cold, at night and after being on the motorway for at least an hour
2. Throttle feels a little stiff throughout its travel for a few miles before jamming
3. When it jams it really jams, I have tried physically pulling it back with my hands and feet and I cannot make it budge
4. When I pull over and turn the engine off (or turn the engine off and then pull over as I have had to a few times) it mysteriously un-jams itself - so every time I have pulled over and had a look under the bonnet the throttle has been moving fine, and if I check the pedal that is also fine - although I haven't tried turning the engine off and on while still moving yet.

Any ideas what this could be? I'm going to go and put some oil on the cable to try and help the situation but I am really unsure as to how it jams so hard and I cannot move it, and then mysteriously unsticks every time I pull over.

Cheers,
Jake

[Noah]

If in doubt flat out - I see no problem with it....

Check the throttle cable isn't snagging on anything?

[jaydee]

Did you grease the throttle cable?
Because thats exactly what happens when putting grease to the cable...

[carbon]

Jake,

Thanks for giving a really clear description of the problem. From what you have said I would be pretty certain you are getting icing up of the carb. This is why it happens when it is cold (also damp aggravates the situation) and why the problem disappears after the engine has stood for a while (the ice melts).

[charie t]

Have you got a stage 1 alloy inlet manifold fitted? And does it clear the inlet correctly?

Edited by charie t, 03 December 2012 - 07:05 PM.

[jakejakejake1]

The thing is the throttle unsticks almost instantly, the first two times I didn't check the throttle pedal first, but by the time I had pulled over and got under the bonnet the throttle was fine, the third time by the time I had pulled over the throttle pedal was unstuck and the forth time I forgot to check the pedal again but the linkage was free to move, but I would say it couldn't of been more than 20-30 seconds between turning off the engine and checking either the pedal or linkage.

And no, no grease on the cable, I will probably go out and put a few drops of three-in-one on the cable as this helped free up the stuck heater cable my car had when I got it and thats been fine for over a year now.

And yes, I do have an alloy inlet manifold, the minispares one, although the water heating is not plumbed in.

And most of the time the cable is free as anything with no signs of rubbing or snagging or anything.

Cheers for the help

Edit: Clarification

Edited by jakejakejake1, 03 December 2012 - 07:10 PM.

[carbon]

If you plumb the water heating into the inlet manifold this should sort the problem.

As you say, not good to have the throttle sticking open...

[minisilverbullet]

Is this a Spi?

If it is it may not be the cable.

Edited by minisilverbullet, 03 December 2012 - 07:40 PM.

[Noah]

Car in the Picture is a J Reg so 91-92... Must be a carb.

[jaydee]

The water heated manifold has nothing to do with carb icing, which happens in the venturi and not in the manifold.
Check carefully that the cable isnt sticking anywhere, remove it and inspect for corrosion, and clean it with wd40, dont use 3 in 1 oil.
If you get carb icing, try using a standard plastic airbox.

[Alex_B]

Engine earthed correctly? it could be a build up of resistance as the cable is earthing the engine and jams it, then when the engine is switched off the current stops thus it unsticks?

is the throttle cable hot at all?

[carbon]

Carb icing typically happens in cold/damp weather. The venturi in the carb sprays the fuel into the manifold, and any fuel droplets which hit a cool butterfly may condense, and then as they revapourise will cool the butterfly and carb body. If this cools sufficiently then moisture in the air can then form ice and this can cause the butterfly to stick - hence sticking throttle.

Solutions to prevent carb icing are :
- put more heat into the carb, for instance by connecting up a water heated inlet manifold. The icing does not take place in the manifold, but the heat conducted from the manifold into the carb body will help reduce throttle icing
- put more heat into the inlet air. With the old style plastic inlet filter casing (late 60's to 70's) the inlet trumpet could be altered to take warmer air from right next to the exhaust manifold.

Petrol with higher ethanol content will also aggravate the icing situation.

[jakejakejake1]

It is a carb (HS4), and I'm using the standard plastic airbox with a K&N Filter
As far as I can tell its earthed correctly, the earth strap was new about 6 months ago as the old one was past its best (the problem has only happened the last two weeks, which have been quite cold and miserable haha)
the cable didn't seem unusually hot when I checked

Cheers for the help, will go double check a few things!

[mk1leg]

treat yourself to a ST throttle cable these never stick.........

http://www.minispare...px|Back to shop

[tiger99]

I am inclined to agree with carbon that it is very likely to be an icing problem, because of the timescale of it occurring and clearing itself. Connecting the manifold heating will help to conduct some heat to the carburettor, although you may want to disconnect the heating in summer for best performance. Also, if you have an insulating spacer between the carburettor and manifold you could try removing it.