3.5 V8 County SU Carburettors stuck open

[Carslil Jim]

Hi,
I have oiled every moving part and the carbs mechanism wont return to the "stops". I was driving yesterday and just before I got home it caught but then released, but now the carbs are stuck about 1/3rd open.

Any ideas??

[dromader driver]

what type and how much damper oil do they have??

[BigJon]

Pull the tops off and clean the pistons with carby cleaner. They probably have a gunk build up on them jamming them in the bores.

[lebanon]

Check your throttle cable, sometimes it does this.

You can oil it by dismantling it from the engine side.
Hold it to the vertical while spraying WD40 or silicon spray between the cable and its jacket.

[Carslil Jim]

What a good question! There was NO damper oil, and I have now added engine oil which is what I usually use. I know lighter oil ought to be used but I have not had any problems (perhaps until now), using the 20W-50.

That had not fixed the problem as of last night, so i will now pull the tops off and clean the pistons.

The cable seems free enough but I will oil it next if we still have the problem

Thanks to you both for suggestions. I will report as we go.

Jim

[bsperka]

Damper oil is just that ; determines how quickly goes up or down. Engine oil is fine to use if you want slower response. It's not a race car. Dust or dirt on the outside of the piston is most likely the problem. Needles could be bent but this is usually when they have been roughly handled.

[dromader driver]

sewing machine oil worked well in my mini SU's. think it is about 10 wt

[bsperka]

If its an SU then the cable has no impact on the piston being stuck. Only impacts the piston if there is vacuum; that is when the engine is running.

[lebanon]

I have been using ATF oil for the SU with good throtle response.

As for the cable if it is not perfectly free it might keep the throtle mechanism, i.e. butterfly open.

[Carslil Jim]

Last night I removed the pistons and I could see the butterflys were closed....but the mechanism is about 1/8 inch off stops, the accelerator pedal is sloppy and I can see slack in the cable at the carby end. Cleaned the pistons which were easy to remove (ie not stuck). Blowed if I can see what is stopping the mechanism from sitting on the stops.

I will assemble later today and start her up and see if it idles normal or runs fast.

Its a wonderful life kneeling on a padded board across the front of the engine and bending over this problem. I have released the bonnet stay and pulled the bonnet vertical to give me a little more headroom so I can see this thing clearly. I managed to spill engine oil all over the place while flailing around with this problem. Competence is coming into question!:)

[bsperka]

So you haven't been using your engine at wide open throttle then ;). Had an issue like this on someone's car. 1/3 throttle at nest. They thought that was just how little power it made; fixing the cable changed their opinion of the car's performance.

[Lionel]

Blowed if I can see what is stopping the mechanism from sitting on the stops.


Back in the dim dark past I had vehicles with SU carbies. I seem to remember that if the needles aren't centred in the jets they will stick & not drop properly. Worth checking the needle mounting points, which IIRC are spring loaded, (or was that Stromberg CD's :(), to make sure that they are free moving. Can't remember whether there was an adjustment for the jet bases to allow centering. Too long ago!

As previously mentioned, a good clean out of each carby, & careful re-assembly should do the trick.

Cheers,

Lionel

[Carslil Jim]

When I came back to the carby today it was resting against the stops. We can consider this case closed (though when I went to test drive it, she started on 6 cylinders, but I have obviously bumped leads while working on the carby). At least the engine dropped back to idle with the choke off.

Thanks again for contributions.

I will sort the missing cylinders in the next few days.