Arduino Mega PWM problem

I've been trying to use the PWM ports on the Arduino Mega to send 75% duty cycle pulses to 2 H-bridges where each H-bridge controls two motors (4 motors in total). Two of the motors will run properly when using the PWM signals and the other two do not turn on. In order to check if the ports would run at all, I kept the PWM signals that were working the same and set the ports that were not working HIGH. After that the two motors ran at the modulated speed and the other two ran at full speed. I want to know if there are other ports that are supposed to be used for PWM aside from ports 2 - 13 like it shows on the board. The arduino website says that there are supposed to be 14 digital ports that can be used for PWM.