Hi Alceu,
That sounds like you might have the cyclic trimmed well back. The real Bell doesn’t have trim, but IIRC it was added as a bit of a cheat, to allow people with shorter/more tightly sprung joysticks to cruise more comfortably.
It may be that you had accidentally trimmed for excessive nose-up and that is causing the issue. Maybe check your bindings and neutralise the trim, before taking off again.
Cheers
Paul
Edit: maybe Heli suddenly pitching up - General Forum - FlyInside Helicopters Forum (flyinside-helis.com) will be of some use.