1972 E Type 2+2 V12 Running on B Bank

I have the auto above. I bought the non running auto in 2018, fixed her up, tuned her and have greatly enjoyed her since (5000 miles); until recently.

Reading the forms back in 2020, I came to the conclusion that the factory OPUS was prone to failure so before I was stranded roadside I purchased a SNG Barrett “Ignition Conversion Kit DAB113 HE” from Terry’s Jag as it was less expensive (Ya I don’t know how that works either.) in July of 2020 and installed it in August 2020.

Ok, that’s the back story. The other day, driving 33 highway miles to my destination; great. Driving 33 miles back home, not so good. I checked all the spark plugs. Bank “A” was like someone stuffed and coated the spark plug electrod ends with white chalk. Bank “B” looked to be good if not just slightly rich. Cleaned all the plugs and reinstalled. Car ran well.

Today 33 miles to destination all good. Driving back; same problem; good for 10 miles then the engine tone, the power etc was half. Car still ran. No accelerator response. Backfire thru the exhaust a few times. Pulled all 12 plugs again. Bank “A” spark plugs no chalk but white. Bank “B” same, slightly rich.

I took the top of the Bank “A” Zeinith carbs off to check the rubber diaphragm on both carbs. All good. Cleaned and reassembled.

What is the problem?? My guess is the DEH ignition. But can this system fail by the cylinder bank?? Doesn’t make sense. I have one coil which seems to be good for Bank “B” so it HAS to be good for Bank A.

I checked the distributor cap just because. Looks fine. Anyway how would a crack develop on exactly every other cap post. Not likely.

I am at a loss and need help.

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Unless you have a Marelli ignition (which you don’t) then, as you said, it would be very difficult for an ignition system to kill just one bank. Actually, since only one bank is affected, that narrows down the potential causes, since the engine is effectively four 3 cylinder engines. White sparkplugs can be caused by lean running, and the throttle bellcrank controls the banks separately. Perhaps the throttle plate spindle is loose from the actuating arm on that side, and allows the throttles to close by the return spring. White plugs can also be caused by a water leak into the combustion chambers, but I don’t know how coolant would get into all cylinders equally. There are LOTS of vacuum connections on that engine, and a vacuum leak would cause lean running. On mine one of the short hoses that leads up between the carbs and connects to the gulp valve pipe had disintegrated, which led to some interesting symptoms. If you have not replaced all the 50 year old rubber on that engine then you should.

Thank you for the reply.

The bellcrank is smooth and tight and moves the LH and RH throttles just fine.
The car did not run when I bought it. I changed all the coolant lines. The air pump was rusted solid so I removed it and the associated air injection rail. I also replaced all the vacuum lines at that time. Since then, I find the vacuum hoses are for valves that I don’t use so I removed the lines and plugged them.

There are 6 ports on the LH side; 1 front 1rear intake manifold, 1 larger port in between the intake manifolds, 1 on front carb, 1 on rear carb, 1 larger port under rear carb. Someone pls verify.

There are 5 ports on the RH side; 1 front 1rear intake manifold, 1 larger port in between the intake manifolds, 1 on front carb, 1 on rear carb. Someone pls verify.

I did not replace the fuel lines. I will do that next thinking that HAS to be the issue. Can’t think of anything else.

Did the SIII V12 E Type had air injection or is it an XJS / SIII XJ fuel injected engine?

It has 4 Zenith Carbs and DID have air injection. I removed the air injection as it was rusted beyond repair. The car was running just fine for thousands of miles. It is just recently the issue popped up.

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