Due to low barometric pressure, the compensating piston in the starting device became stuck, preventing the helicopter turbine engine from starting on a remote island. The engine cowlings were locked in an open position, and the pilot initiated the engine start while I was tapping the starting device with a piece of wood, which released the compensating piston, allowing the turbine engine to start. The cowlings were closed with the engine running, and we returned home safely to replace the faulty part.