I am just guessing, I don't know efi too well. When they first came out in cars, my father used to try to start one wil his foot on accelerator which put it out and then would stall. Now they have minaturized them enough for scooters, but I have no experience with them myself. I think they work by sensors near intake and exhaust (lambda sensors?). You might try testing those perhaps, the manual might give a resistance values to check with multimeter.
I am only guessing but trying to be helpful.
edit: would you get an error code on the display if EFI malfunction?