I try to start my ninja 300 but it only starts if its revved above 3k rpm ,getting difficult, and even though while moving doesn't matter the gear if the revs comes between 1-3k its shuts off, again then have to switch start it,
Might be a dumb question, but is the idle set too low? There's a little screw adjuster on the left side of the bike, accessible through one of the holes in the fairing. I know at one point mine would die at idle, I turned the idle back up to where it was supposed to be (1300 I think?) and that fixed everything. Don't know if it shook loose or if I inadvertently frigged with it without paying attention, but that's all it took.
If it's dying at like 2k though, this isn't likely to be your problem.