Gonna need a bit more detail before I can help you.
What is the tumbling pass? I can give a lot more specific suggestions if I know what skill you're doing.
Assuming we're referring to some sort of salto element, you should take off with your head neutral and your arms approximately vertical, and try to hold that position until you're clear of the floor. Throwing your head doesn't make you rotate, it just makes you feel like you're rotating. With any flipping skill, 90% of the time the best way to improve it is to work it on a trampoline.