front disc brake conversion

first of all i had a mechanic install a power front brake disc conversion kit on 72 plymouth duster. it had manual brake all around. i purchased the kit from pirate jacks. everything seemed to go on ok he bled the brakes followed instruction from the kit. i still dont have the stopping power i thought i would get...did he overlook something..if you can keep it simple when explaining the problem or solution would be appreciated..i am not a mechanic,sorry.. any help will be appreciated. thanks arab