Good afternoon Team Jaguar/Daimler, and an especial warm welcome to the V12 owners.
I have a Series 1 Daimler VDP Double Six (ostensibly the same engine as the Series 3 E-Type engine). The car had been running poorly for some time, lacking power, not starting reliably: hot or cold, backfiring under acceleration, and most embarassingly stalling at idle, or stopping intermittently when coasting at low speed.
Fault Isolation:
a. took the carburettors apart, and rebuilt them with SU/Stromberg kit. Several problems identified:
i. temperature and vaccum bypass valves full of soot, rebuilt these and reset to the factory tolerances;
ii. needle settings in various states of adjustment, but varying significantly;
iii. float valves dirty, float bowl had a sand like substance in them;
iv. Fuel inlet gauze filter blocked with what looked like silt.

b. Despite rectifying all these problems the car improved, more power, started better, but still exhibited the same symptoms.
c. Vaccum advance wasn't working, bought a new one;
i. Problem still evident but much improved power.
d. Stripped down distributor, looking for damage of siezed mecanical advance etc. Removed all spark plugs, and examined colour/condition.
i. Spark plugs were significantly different in colour, however found that they conformed to a diametrically opposed pattern i.e. the sooty ones were opposite to each other on the distrbutor sequence, whilst the sandy good burn ones were also opposite each other on the distributor sequence;
ii. After closer examination it appears that the bushes in the distributor were worn, and the rotor arm was taking a slightly eliptical path inside the distributor cap, making good contact with some parts of the dsitributor and hardly any/intermittently with others;
iii. I had a spare unit from a Series 2 V12 I am restoring, and replaced the faulty unit;
iv. Replaced the plugs with NGK (do not use any other plugs in your V12, they are not equivalents);
iv. Retimed the car

Problem has dissapeared.
Regards,
Chris

 

Dizzy’s are always overlooked. Great work!

 

I just completed the same process with my carb'ed V-12. This post will be helpful to future searches so thanks for sharing.