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My '70 Series II E-Type has developed an annoying miss that's most noticeable at idle and at steady, low speeds. I was unsuccessful in diagnosing it ao I took it to a local "expert" who told me that my vacuum retard unit is out of commission (I already knew that...the diaphragm is shot and there's no connection to any vacuum source anyway) and that the lack of retard causes a "flat spot" on acceleration. My vacuum retard unit was disconnected when I got the car seven years ago and I never fixed it...and so I am pretty sure it's not the cause of the engine miss, which cropped up only recently. My question: Do any of you Jaguar guys know the performance effect of this thing (and where the other end of the vacuum line is supposed to be connected...under the front carb?...to the rear of the inlet manifold?) I'd appreciate your advice._
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E-Type ignition
- Thread starter Lee
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I can't reliably answer your question but how recent were the plug leads changed or the plugs gapped. The leads may be shorting or just deteriorated sufficiently not pass a low voltage spark. The same for the plugs and when the RPM's increase the voltage is sufficient to overcome the resistance. Nothing like an intermittant problem to challenge the brain. Paul
The vacuum advance unit (not retard) causes the timing to advance under small throttle openings, and is an economy device. Strobe setting of the timing is done with it disconnected, but at idle and with a functional unit the timing will be advanced from that setting. Your car, therefor, will be running retarded from the factory setting.
I don't think that will be the cause of your misfire and I have run cars before without the vacuum advance being connected.
I think that you will need to run a basic check of ignition and carburation. Also is the engine sound mechanically, e.g compression?
My Jaguar (MK2 saloon) has the vacuum pick up point on the front carburettor.
Alec
I don't think that will be the cause of your misfire and I have run cars before without the vacuum advance being connected.
I think that you will need to run a basic check of ignition and carburation. Also is the engine sound mechanically, e.g compression?
My Jaguar (MK2 saloon) has the vacuum pick up point on the front carburettor.
Alec
Thanks Piman. It is indeed a "retard" unit (Lucas 544422224) and was fitted only to late 1969 and 1970 model E-Type Series II's (possibly only those sold in the USA). It is supposed to have had some emission control purpose, but I don't know what it was, and haven't been able to find any literature that helps. The confusion is compounded by the fact that the earlier (1968, early 1969) emission-controlled cars used the same cams, ignition components, and carburetors, and did have vacuum ADVANCE units. If I could re-pose the question, I guess I would ask "why do I need a vacuum unit at all, and could I retrofit an earlier (vacuum advance) distributor to this engine without causing a problem?" This is because I suspect I could buy a complete used distributor for about the cost of a replacement vacuum retard unit ($200+ from USA sources).