Leaping Jaguar

Fuel

Jaguar was forced originally to use four Stromberg CD175SE carburettors as fuel injection from Lucas only finally appeared in 1975; based on Bosch L Jetronic system. Strombergs were chosen over an all SU set up due to stringent emissions laws at home and abroad, especially USA and in particular California.

In fact, the XJ12 was the first automobile necessitating Air Emissions Control in UK. When you analyse this engine in detail, you realize that moving and warming over 20 litres of coolant is no mean feat. It needs to warm up fairly quick for decent fuel atomization, made harder by carburettors.

My engine was no different, still equipped in EGR (Exhaust Recirculation System), air pump and all the plumbing, used to inject pressurized air in exhaust ports, in order to impoverish unburned gas. All this system was ditched as it really penalized performance without any real effect in reducing emissions.

I initially bought a Burlen Fuel System kit comprising of four SU HIF44 and all its ancillaries, renowned as the ultimate SU carburettors, with its integrated fuel bowl, jet exterior adjustment, easy servicing and superior performance.

I modified further these carburettors with richer needles (0.100" floating type) and lighter springs (yellow 4oz) for faster response.

Unfortunately, my engine is fitted now with radical camshafts which penalize carburettors performance, with its weal vacuum signal and intricate inlet manifold design, coupled with poor fuel atomization when cold; it really is a struggle to start the engine from cold. Once warm, it is wonderful, incredibly quick through the rpm range.

I was forced to remove this wonderful set up and fit it in my XJ12 SII where it does a sterling service.

Having rebuilt the twin SU double body (AZX1405) pumps in the back, its points operation and propensity to leak did not convince me, even after I fitted an electronic contact breakers kit from Burlen. For much less expense, I fitted twin Facet Red Top pump, much superior in flow pressure and fuel debit. Their pressure is phenomenal as my Filter King fuel regulator was having trouble to keep pressures bellow 3 psi!

All flexible pipe work is braided in stainless steel finished off by flashy hose clamps by Spectre (USA), should last another thirty odd year I would think. Solid pipe work in the engine bay was chromed plated and all the rest zinc plated.

Fuel tanks were sandblasted, lead loading repaired around the inlet neck, powder coated and rust proofed inside with POR-15 products. Drain plugs were replicated in 316 grade stainless at great expense. All thermal sensitive areas were covered in high temperature aluminized mat, as used by rally cars to prevent fuel vapour lock and excessive temperatures. You can see in the photos the exhaust manifolds being wrapped, starter motor receiving a specially made thermal blanket, heat proof original panels such as bulkhead and rear silencers spaces were recovered in this extremely effective material.

It sports an interior gauge for fuel pressure out of AC Cobra, for which I took great care to buy a pressure sensing line for high pressures, thickly braided in stainless steel, with I then added thick clear rubber hose all along its length to stop rubbing/damaging itself along its course form the front of the engine to the centre console. It certainly looks the business.

I've also acquired a AFR (Air Fuel Ratio) gauge along with a Lambda sensor from a BMW K1200RS so I can monitor at any time the fuel mix, although it will only confirm this engine runs best at 11-12:1 ratio, quite rich for the ideal stoichiometric point of 14.7:1. It may be used later along with a second Lambda sensor for the other bank of cylinder to monitor and inform the ECU of data needed.

As the original inlet manifold is quite long and has an awkward design where the carburettors bolt to(separate manifold with a coolant jacket for quicker warm up times) for best low range torque, it is not the ideal solution for a high performance engine with a peaky cam.

So I did purchase an old EFI manifold from early eighties which I'm cutting and ditching the original 2 throttle bodies and I will modify it to accept 12 independent BMW K1200RS 39mm throttle bodies, along with a MegaSquirt ECU and an alloy handmade air filter boxes. High pressure fuel pump will be employed, most likely a Bosch 210 item or a Sytec. Will still use Facet pump to extract fuel from tanks and keep the recirculation solenoids but a big swirl pot will need to be added. All flexible pipes will need to be replaced by high pressure ones along with a myriad of other modifications.

Due to other commitments, the Jaguar has been left in the back burner but as soon I have a bit of time available, I shall follow my goal, even if I need to get milder cams!

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