This car is standard apart from a 123 distributor and a manual choke conversion.

Symptom: from cold, the car will not idle evenly on choke, revs rising quickly to 2000 rpm then dropping quickly to 450 rpm repeatedly. It will do this for 2 minutes or so until the choke is put back in where upon it may just about tick over if you use a little throttle. If you put the choke back out, the revs drop off risking a stall. During this warming up period, it is undrivable. Many hundreds of pounds and hours have now been spent on this problem at a well known Jaguar Specialist garage. A "new" AED did not start the car. ALL electrics have been replaced. New carb gaskets, pipework, Carb overhaul: main jets, plenum springs etc etc.

Once warm, the car runs fine with good emissions, restarting easily.

So, if anybody has experienced such a problem like this and knows the cure, I'd be very pleased to hear from them. Ask your friends! It must be a simple fault that has been overlooked. Remember,from cold, with choke, rising and falling revs down to almost stalling / excessive reaction to slight throttle when on choke is what you need to think about!

Many thanks in anticipation - I am getting desperate now after a year of this problem!

Clive

 

Thanks for the advice, unfortunately, your comments relate to a fuel injected car - my car has 2 HIF7 SU Carburetters and therefore does not have an AAV. Good try though!

Many thanks

 

openend a new thread

 

Assuming the other longshot causes I mention below are OK, you can be pretty sure as indeed the other gentleman suggested, that it is an air leak somewhere. The main suspect is the manifold to head gasket (they notoriously leak around the end cylinders 1,2 and 5,6.

Outside an air leak, another fuel related cause could be from a sticking carburetor piston or even integral float gummed up from standing but this is less likely since you say the HIF7's were overhauled. With the engine switched off, try lifting each carb piston in turn through its full range of movement, check the dashpots are full of oil and that the sliders drop smartly.

There should be a very strong hiss from each carburetor -if there isn't immediately suspect an air leak. Try the old RAC man's trick of using a rubber tennis ball to choke off each one of the carburetors in turn which should stall the car immediately if both carbs are seeing enough vacuum. If the car does not stall, the car is simply not breathing through the carb in question very much proving an air leak.

The diagnosis is to look for very weak and erratic partial piston lift and slide response when watching the SU throats with a mirror on picking up revs on the hand throttle. Usually the car just doesn't sound right and does not want to rev cleanly. Often, the carb nearest the leak is the one most affected and both pistons will not lift in unison. The car dies and splutters since basically it is drawing insufficient fuel mixture due to the carb(s) being bypassed - then it will eventually overfuel since the pots unaffected by the air leak (usually the middle ones) continue to demand fuel from the AED. Flooding and a marked reluctance to restart when hot unless cranked with the throttle wide open after stalling or switch off also often bafflingly forms part of the symptoms. Backfiring in the exhaust and black soot blowing from the exhaust is another common symptom. The engine runs with its mixture strength all over the place with some pots rich and others weak and overall the airflow is strangled through the engine. Also the exhaust can sound almost 2 stroke with an airleak with a chuffing sound.

It is just possible to reach the lower manifold nuts without removing the carbs to nip them up to attempt an improvement but since all else seems to have failed I suggest a new gasket and a three hour job to fit it. Changing the gasket produced a totally different car in my case. At least it is a cheap fix!

Other possible causes: Failure to rev can also be caused by a failing condenser in the distributor. The car starts but won't rev due to it breaking down and sparking across the points. This happened to me after a blast across France but it does not seem like your problem which I agree sounds almost certainly fuel-related. Lastly, being a long stud engine in the series 2 are you sure the head gasket has not failed due to stud corrosion - another common fault on these engines with studs through the water jacket? I assume there is no water loss involved?

Best of luck!