Running Weak

[john lever]

:?Can anybody help?

My car is now resident in France and since last year it has had a problem: when in traffic, in hot weather, it has sufferred from what I thought was fuel starvation, due to excessive heat. I have fitted a thermostatic fan and the viscous fan.The car runs roughly and will not pull away at low revs.

I have found that if I pull the choke out it goes ok, so recently I checked the carburettor settings and found that both were running weak. This would explain why the engine was getting hot.

However, when I tried to adjust thecarburettors with theadjusting tool I turned it to the maximum for a rich setting and the car was still runs weak.Is my next step to try new needles or is it the float chamber, or some other cause?

p.s. I have a (recently fitted)new electronic fuel pump, so think I can eliminate that one.

[StagnJag]

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Have you checked the balance between the two carbs? Mine was always a bit hesitant when I pulled away. I balanced the carbs for the first time on Saturday and it has made a big difference. I haven't changed the mixture settings at all but the emissions results from the last MOT (9 months ago) suggests that it is running pretty lean. Its a bit temperamental when cold but otherwise running very well.

Regards

Dave

[V Mad]

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First check plug colour is white to confirm it is weak. An air leak can weaken mixture (check the connection from manifold to air filter box etc) as can low fuel/float level in the carbs.

[john lever]

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Thanks

I think they are balanced - I use an old fashioned technique - a piece of tube and listen to the hissing noise. A bit crude but it has worked in the past. I have a carb-balancer also. I will re-check them with the carbbalancer when I return.

[john lever]

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It is possible that I have a (slight) leak on the inlet side but I can't find anything. My guess was the float chambers and I bought new gaskets to do this. Removing the carbs is fiddly, so I thought that I would try new needles first - but they are not cheap. Probably stick to the original plan.

Spark plugs diagnosis is more difficult, because I have to keep pulling the choke out when the car is stationary, which causes it to run rich.

Very frustrating, because the car runs and ticks over perfectly when I play with it but the problem startsas soon as I have covered about 20 miles and I get stuck in traffic - fortunately that is not a major problem in France.

Thanks for the advice

[Sheepdip]

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Coincidentally I had similar problem couple of weeks ago. I'm running on borrowed carbs as I work on mine, never really set them up so a bit rough but work ok and been like that since last summer.

Been running since beginning of April but suddenly it started and ran ok at speed but once really warm, slow tickover and no power, I had trouble getting away on a hill with the auto.

I pulled the carb covers off and really cleaned, the piston and carb innards as wondered whether sticking. I changed one of the diaghrams, no holes butan area that looked dubious. I also richened one carb as evidently different from the other, but it must have been like that last year.

And it all works fine now. Worth a try

Good luck

Paul

[john lever]

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Thank You

Problem is now solved.

One carburettor needle was sticking. I was told that it was the silicone in the petrol that causes it to stick after a long lay-up. I was advised to clean with wood burner window cleaner, which I did and the car now works fine.

[V Mad]

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Glad you solved it but I am puzzled about your sticking needle. Do you mean the needle valves in the float chambers?

[john lever]

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No. it was one of the carburettor needles. I fitted new needle valves in the float chambers and new carburettor valves but it didn't solve the problem. When I was setting up the carburettors, I noticed that one of the needles was sticking slightly but didn't think anything about it. Anyway, I took the car on a run and there was no problem. I left it for the Controle Technique (French MOT) and when I returned there was a very frustrated mechanic. My car was on the rollers but it kept cutting out when he tried to do the tests. Eventually he abandoned it and I was stuck with the car at the testing station. I then remembered the sticking needle and backed offthe carburettor dashpot cover screws a minute amount and the car started and revved perfectly.When I mentioned it to a mechanic later that day, he said immediately that the problem was with the petrol and to clean my carburettors thoroughly. (when I changed the needles, they looked as clean as a whistle) but when I examined them after the incident, I did notice staining in the carburettor that was sticking. Needless to say, I took it back to the MOT Station the next day and it past - no charge for a repeat and two years. Since then I have taken the car on a 200 mile round trip in 25 degree sunshine and the car ran perfectly - so I am now delighted.

[Tdm]

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Are French Testing stations like those in Spain where no allowance is made for Classic cars as regards CO2 emissions?. Mine failed on emissions some years ago and I had to weaken the mixture as much as possible to get it through.
Left it alone since then and apart from always needing full choke to start from cold, once warmed up it runs fine and when warm will restart without any choke.
It is not quite as responsive as it was before the mixture was weakened - but I can live with that.
In 2012 when my Stag will be 35 years old I only need to have it tested every 5 years instead of every year as at present. Don't see the logic in that but it suits me and will save me money.

[john lever]

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I don't know about the emissions. I thought the car had failed because they produced a list of faults - including an auto-gearbox oil leak - which every Stag suffers from. But it passed. The print-out gave CO at .99, CO2 at 12.9 and COC at 0.99 (whatever that means).The test is valid for 2 years and costs 60 euros. If the car fails, you are allowed two months to rectify the faults and the re-test is free. It is possible to register the car as'historic' if it is over 25 years old. This restricts the driving to the local departments but means you only need an MOT every 5 years. I have not registered the car as such.

After my 200 mile round trip, I removed a plug from each side and one side was running weak. I then removed another plug from the same side but other end of the engine and it appeared normal, so I enriched that side by half a turn. Next time out, I will check again.

Overall, I would say it is running weak as I am returning 25 mpg in an automatic.

It requires full choke in winter but, in summer, as soon as it starts it will run virtually without any choke. - so the setting can't be far out.

[V Mad]

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john lever wrote:

After my 200 mile round trip, I removed a plug from each side and one side was running weak. I then removed another plug from the same side but other end of the engine and it appeared normal, so I enriched that side by half a turn.

I assume you know which carb feeds which cylinders (its not immediately obvious)?