Practice long tones working your way up the register- often (I find) a player just needs to accustom themselves to a new instrument. This tends to be more important with bass clarinets than with sopranos, because basses are often more finicky.
If that doesn't help, try checking the keys and making sure they are all covering how they ought and opening when they should.

Good Luck- school bass clarinets that don't work suck!