Too much elevator throw will cause the plane to flip over on its back and go out of control. If it's unintentional, it's called a tip stall, and if it's intentional, it's called a snap roll

Control linkages are like gear ratios. The longer the "driving" arm, the larger the throw. The longer the "driven" arm, the shorter the throw. Move the pushrod closer to the pivot on the servo arm to reduce your control throws to the recommended maximums. If that doesn't do it, move the pushrod out away from the surfaces on the control horns at the elevator and rudder.

As Matt says, use the ATV to reduce the throws only after you have them mechanically adjusted to the recommended maximum.