This vehicle is owned by a classic car enthusiast who normally does all of his own engineering, and baseline tuning.  However, when it cam to a V12 engine fitted with 2 sets of twin carbs (ie...4 carbs in total), he needed a little help with all the balancing and juggling involved to set them up correctly.

On arrival the car was warmed up from the journey and idling between 1100 to 1300rpm (as per the above video).  The typical book spec for the Jaguar V12 of this era is that it should idle in the region of 650 to 800rpm, depending on what draw is placed on the engine, perhaps from such as A/C if fitted.

So the first task was to baseline all 4 of the Zenith Stromberg 175 CD2SE carbs, synchronise and balance all air draught/draw requirement, jet heights, choke air draught, and fast idle.  There is then the interconnecting activation rods, between pairs and across to the opposing 6 cylinders on the other bank of the V12 engine which also need balancing for synchronised operation.  Together with some tweaks to the ignition timing, the idle speed could be brought down to a nice and healthy 725 to 750 rpm,  with full Choke/Fast idle set at 1200 ~1300rpm.

A beautiful engine to work on, but there's no getting round the fact that the more cylinders and engine has the more tweaking, balancing and optimising is required.  As you'll see in the video links below, afterwards she 'purrs' like a true Jaguar E-Type should, and was super smooth as this V12 engine is renowned to be when set up correctly.

The below video is of the big V12 ticking over on fast idle from a cold start........That's a proper Jaguar Purrrrrrr!!