Like sinker said, as soon as there is a tie on the roll, the defender gets 4 stress from the weapon. The defender can't benefit from his weapon, unless maybe with a stunt. For the attacker, the weapon only gets added to the stress, if his attack succeeds (or at least connects), it does not get added to the attack roll.
If you already did all that, and the defender always won, then that was one (un-)lucky fight. Maneuvers are the way to go, changing the pace of the fight, when the opponent is of equal strength.