An appeal for help

[Alan]

To get the right needle position, screw up the jet adjusting but until the jet is level with the “bridge” in the throat of the carb. ( I guess you know this anyway) then screw it down two turns. (12 flats) that is where the needle is designed to operate. If you can’t get it right within a few flats, really you need a different needle. My Chummy runs on A BY needle which is quite a bit richer than GG.

[Mick Hanna]

Thanks - very instructive.

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Thanks - very instructive.

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Thanks - very instructive.

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Thanks - very instructive.

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Thanks John - I'll try to sort out the SU and fuel delivery first, then look elsewhere. Just watching a Gunson Colortune on eBay at the moment which might help diagnostically.

Lowespeed (Andy?) The float level is good and the needle valve seems OK. I have a copy of the SU Manual which I'm using.

[Mick Hanna]

Fellow Austineers,

I'm not sure if I should be embarrassed or ecstatic, but working through all the advice and suggestions you have offered over the last few days, the Ruby now runs without choke and sounds (almost) normal!

'What did you do?' I hear you ask - 'Was it my diagnosis that proved correct?'

I checked for leaks on the carb. induction side using the oil/WD40 test for leaks - although nothing showed up I replaced the SU carb to adapter gasket and adapter to manifold gasket and checked the exhaust manifold nuts for tightness.

Since my initial problem was sooty black plugs leading to an engine that wouldn't idle without choke, I thought I should begin by adjusting the jet as described and swapping the needle to a richer one (AN), skipping the in between EN needle. 


But before starting on this I decided to check the condenser (Yes, I know, it had been suggested by a few of you). In my head I had rejected this idea because the car was fitted with the electronic unit which confused matters by failing - I subsequently refitted the original manual distributor with its fairly new condenser. I had saved the old one and decided to swap them anyway, just to see - I didn't want to rule anything out. This is where the embarrassment comes in - it started and ran without choke.

Many people have told me not to fiddle with things if they're working alright, but the mixture on the SU was still not right so I've changed the needle (as above) because it was running weak. It needs a road test to set it up properly (fingers crossed), but being cautious this will involve running the car round the block in ever increasing circles until I'm confident I can get back to the garage.

In conclusion, so long as this is not a random and happy blip in events, I might make it to Autokarna this year!

Many, many thanks everyone.

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PS. That should read EB needle, not EN

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PS. That should read EB needle, not EN

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PS. That should read EB needle, not EN

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PS. That should read EB needle, not EN

[JonE]

Nice stutter!

Well done.
So it's on an AN now?
Out of interest, did you have an event which caused the electronic failure... i.e. when you were fiddling with wiring and perhaps had a loose connection?

[Chris KC]

For what it's worth my Ulster rep has been running on an AN needle (and 'red' spring) for a long, long time.
I'm not sure this is optimal and I have plans to experiment with it; but it should work OK.

[Mick Hanna]

Hi Jon,

I had the car running on high revs just to keep it going and turned my back on it for about a minute chasing up a distraction and it just died. Of course I immediately thought it was a fuel problem, but I was able to test the electronic distributor on the bench, later. All part of the developing saga which I hope is now drawing to a close.

I think the stutter might have been caused by using the 'back arrow'.

Thanks Chris - very reassuring. I've been very mindful of the SU advice offered. I believe my spring is a blue spring.

[Dennis Nicholas]

Just to bear in mind for all that running weak will cause overheating. Probably of more relevance to higher powered cars which should run on higher RON than current unleaded basic. e.g 75 instead of 78.

Dennis

[Ian Williams]

Blue spring will suit most applications and it is unlikely that anything heavier then red will be required, also worth bearing in mind when playing with SU needles that the the basic set of profiles are the numbered ones, from there on all others are created for specific applications. The old rule of thumb for a fast road/race tuned seven on an 1 1/4" SU was blue spring and number 5 needle, this was very close to ideal in many cases. I appreciate this is somewhat academic regarding Mick's question and application, but may be of help to others reading.

[JonE]

mintylamb.co.uk is back up for SU needle comparison. but not as good as it used to be.

[Hugh Barnes]

It might just be worth mentioning, for the uninitiated, that not all SUs require a spring. The earlier series, such as the OM that I use on my cars (that come from a pre-war Morris Minor) do not have a spring fitted...