AWSOME!
Thats really wierd you cant run it with stock injectors?,I definitly ran on mine!...I would have thought it would have been worse with 600cc ones!? be very careful with WOT(open loop) the ecu will expect to see 280cc...it may just run really rich!

Just incase(only because i did this initially) did you disconnect the FRP vaccum to set up the pressure?...if not that could be your problem with stock injectors.
I did mine by bypassing the fuel relay and setting it up with the engine off...however im sure its just as easy to remove the vaccum and plug up the hose into the plenum while you adjust to ~43psi.