Hi spirro welcome to the site. What car do you have and what engine? What make of air filter is it?
I'm guessing its a low cc engine and the loss of power is typical when you fit an induction kit. A panel air filter would probably be best for your car.
It may also be down to the exhaust - more air in means more air needs to get out so if the engine size is larger it might just be an exhaust issue.
