The difference between your setup and mine is the location of the injectors; I'm using a SPICA manifold, which places the injectors in a fairly modern position much closer to the valves, while you've got throttle bodies with built-in injectors mounted much further out.
This only makes a difference when my engine is cold as the fuel tends to puddle a bit on the cold manifold. This makes driving a little sluggish for the first 10mins ( still nowhere as bad as carbs), but once things warm up there's no problem.
Still, I've got what sounds like the same driveability glitch, with a slight lag when tipping the throttle in after running with the throttle closed.
Have you tried xtau? I found that it ran a lot better under slight accel and deccel with it on. I also have the AFRs in the run down area (below 70kpa) fairly fat, 14.7, and this helps a lot too. I only get a slight hesitation under particular situations, eg certain RPMs and MAP, the rest of the time you wouldn't pick it from any other modern EFI engine.
I'm sure with a bit more fine tuning I'd eliminate it but can't be bothered as the engine with be coming out in a month or so.
So, the SPICA system sequential, yes? Megasquirt can only support batch-fire injection. I'm wondering how much driveability is down to this difference.
I very much doubt it. Many other twin cams with ITBs run fine with MS.
Most of the advertised advantage of EFI (more effiecient, cleaner, can run leaner, etc.) seems lost on the Nord engine and individual throttle bodies. It simply wants a ton of fuel dumping in at all times to maintain driveability and responsiveness.
That's the nature of the little beast. Still, I get some very good MPGs out of mine. Much better than when I had carbs and never plug fouled either.
As for your erratic MAP signal... how bad is it? Do you have a common plenum, too?
No plenum, just restrictors. At idle it jumps around a couple of kPa but is pretty smooth when driving. Only problem I have is that small variations in throttle make big changes to MAP. I think this is down to the TBs being oversized.
That said, the MAP signal strength is weak: about 75 to 80 kpa at idle, and jumps right up to 98 or so with the slightest whiff of throttle. So most of the "working area" in my fuel table is from 98 to 101 kpa. Hmmm... I'm surprised it runs as well as it does.
I'm about 70 at idle and 75 to 85 normal cruise between 1500 and 2500 rpm. Goes up about another 5 at 3000 rpm. Open the throttle a bit and it quickly goes to 95-100.
In the end your 3D VE table should resemble a skate board ramp with the VE quickly rising above 85kPa.
I've even seen some ITB VE tables with a little ramp at the lower end of the MAP range (below 30). This may give some insight into other people's problems with rundown fuel loading.
And yep, given the limited range of the MAP signal its very surprising how well you can get these things to run on speed density.