The pilot's inadequate preflight inspection, which failed to ensure that the left fuel filler cap was secure, and his decision to continue flight with a known malfunction in the electric fuel pump. Also causal was the pilot's improper positioning of the fuel selector to the both selection after the siphoning fuel condition was noted from the left tank filler opening, which resulted in fuel exhaustion.

A loss of engine power due to the eventual loss of electrical power which resulted from the pilot's failure to ensure the alternator switch was on as specified in the before starting checklist. The inoperative alternator out warning light was a factor in this accident.