Ok so more progress!!
With everything where it should be, it doesnt go, BUT... If I disconnect the tube for the MAP sensor, it starts and revs up running very rich, bogging down when you open the throttle (if you're gentle then it can happily rev up) backfiring and all sorts. If I have it running and reconnect the tube it dies.
Any ideas anyone? A weird one for sure.
Side note, i have actually continuity tested pretty much every single cable to every single item on this bike, everything goes to where it should and all sensors tested give the correct voltage/resistance according to the manual, including TPS, intake pressure sensor, crankshaft, Cam, atmosphere, water temp, injectors, coils, fuel pump and relay, and intake air temp.