We report > 13 MHz/mW pump power efficiency in increasing the repetition rate of passive harmonic mode-locking by engineering the soliton pulse energy in Er fiber lasers incorporating carbon nanotube saturable absorber. Stable pulses with a similar to 5 GHz repetition rate and 40 dB of super-mode suppression are demonstrated with only similar to 400 mW pump power in a single-clad fiber laser. (C) 2012 Optical Society of America