it may be that you do not have the line pressure high enough.. If you are sure you have no air in the lines... try pumping the brakes several times...then with your foot still on the brake pedal activate the line lock.. then push down on the brake and deactivate and activate the line lock again...you should then have lots of pressure on the front brakes.. Remember that when you get on the gas don't be shy..Get the car "up" on the tire
Good luck