Engine rebuild - start up problems

Hi, there's a long story to this, but I have fully rebuilt a Jaguar V12 to OEM spec and better (bigger valves), running a Haltech Elite 750 ECU. It's had previous tunes on Dyno before rebuild. It is a bit touchy to set up the timing, as the timing sync signal comes from the distributor, and runs a single smart coil. It's impossible to confirm timing set up if engine won't run! Engine will crank, it 'catches' and runs for a few secs and in one case close to 15-20 secs before dying (confirmed oil pressure at least!). I suspect the issue now is the base fuel VE table, the current base fuel table has low VE numbers at low speeds (15-20%), I suspect even with all the correction factors for cranking and post start, I am starting to believe it's not getting enough fuel to sustain fire and run. Engine is tight and you can feel each of the 12 compression strokes as you turn it over by hand! My question is what sort of VE improvement could you expect especially at low speeds for a 'new' engine compared to an old fairly worn one! A 50% improvement would mean significantly more fuel by the time correction factors are applied and I can't just play around with the correction factors such as cranking and post start as they only work for limited times. I can increase the temperature correction but that only masks the problem. Interested in any input based on experience to get things going!

Any real reason you can't pull the plugs, and using a fully charged battery (and jumper if required) crank it over to get the ECU correctly timed?

Once that's done, you can set an initial timing point for the ignition - around TDC might work best to reduce 'kick-back'that might slow the cranking.

For the mixture, what do the spark-plugs show - very sooty, shiny black, shiny white, dry white, or what? Can you smell petrol from the exhaust? Have you tried - carefully - squirting raw fuel into the intakes of the throttle bodies? Oh, I assume it's the later model with the fuel injection rather than the SUs?

Any black smoke from the exhaust?

I assume you've done the basics, like checking the spark-plug firing order and wiring is correct? I assume you have the bodies, or carb's, reasonably closely synch'ed - a feeler gauge between the butterfly and body works quite well for the mechanical side?

Oh, have you seen the work "Harry's garage" did with his Jag V12 Coupé - BIG improvement everywhere!

Thanks, yes done most of that, the cranking timing setting idea isn't very accurate, tried that before, yes firing order etc all fine, plugs are new and very clean. Provided timing is roughly right it should run. I'll probably just up the initial squirt and cranking injector volumes, which are all % of the base fuel map, hence the question about what sort of VE improvement people have experienced between a 'worn' engine and a very new one, with tight clearances and better breathing to make some initial adjustments to the base fuel map which might help initial running. Just wondering if there is something in that.

If the plugs are clean, and dry(?), that suggests lack of fuel, period. have you confirmed you're actually getting fuel pressure, and fuel out of the injectors?

I wouldn't expect a significant variation in the air being drawn into the engine (the "VE" concept is barbarous in this context, IMO, and a source of a LOT of confusion, especially with forced induction), and the normal starting enrichment would be expected to counter that, anyway.

Harry's V12 coupé with the upgrades - https://www.youtube.com/watch?v=m690xQJA7-I