| Centrifugal Advance (Ref pg 92):
When I purchased this car the previous owner and I noticed the lack of pulling power. How can a V12 be so anemic! Well the advance mechanism seizes up due to a bad choice of lubricant. The owner can determine this by twisting the rotor arm, if
the rotor arm does not spring back you have a problem. Remove the distributor, disassemble, clean and lubricate. If the owner wants to avoid damaging the engine due to overheating, this job is priority number 1.
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| Distributor Vacuum Advance (Ref pg 89):
The vacuum advance on my car was also US. Apparently the heat destroys the bellows. I purchased a new unit but is not easy to replace with the distributor in the car. To test this item connect a pipe to the nipple shown and suck. If the
mechanism does not retract and move the rotor arm then you need a new vacuum advance assembly. This repair is only applicable for models up to an 88. The newer Marelli ignition system on an 89 onward has it's own problems! Check the timing
when complete.
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| Rotor & Distributor Cap (ref pg 83 & 100)
When replacing the rotor check that centrifugal advance mechanism is working. Also lube the felt pad in the center of the distributor. When refitting the distributor cap ensure the
two vent pipe connections are fitted, yes vent pipes. The
picture shows the white protrusion on the side. The upper
connection is obscured by the cables. While the
cap is off check the pick up gap, ref pg107.
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| Ignition Timing (Ref pg84):
The timing should be 10 deg BTDC with the vacuum disconnected and at about 600 to 700 rpm. The timing is best tested at 3000 rpm because the owner is interested in the timing when accelerating not at idle, ref Kirby's book for the timing
specification. Not a pleasant job checking the timing under the car with the engine and cooling fan rotating at 3000 to 4000 rpm. This is a great opportunity to check that the advance mechanism is working.
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| Spark Plugs (Ref pg78):
On most vehicles this is an easy job. On a V12 XJS, replacing the spark plugs is NOT an easy job.
This task will take at least a couple of hours. See Kirby's book at pg 78 for all the gory details. BPR6EFS are the regular plugs, set the new
plug gap to 0.025 inch. Setting the gap higher will result in a
misfire at high RPM's. I used the Bosh +4's Platinum plugs
on one of my cars and the platinum Autolite on my other car. Use
Platinum because this is a tough job and it best only done once.
The Bosh Platinum +4's did not work well with the regular ignition
wires. I only suggest this option if you purchase performance
ignition wires.
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XJ-S H&E
Jaguar Repairs and Modifications [Ignition components}