The pilot-in-command's failure to follow emergency procedures to reduce drag and maintain best climb airspeed. Factors were the partial loss of engine power due to the cracks in the #1 and #4 cylinders as the result of an unapproved modification of their intake ports, the separation of the magneto lead plate due to its improper installation by the pilot-in-command, the dark night light conditions and the lack of suitable terrain for the forced landing.