The pilot was carrying out a check of the station windmills prior to commencing mustering operations. About 15 minutes after DEPARTURE he reported that an acrid smelling gas entered the cabin. He turned off the radios, the master switch and closed the cabin air vent and diverted to the nearest suitable strip. Enroute the acrid smell intensified and as the pilot was having trouble breathing he decided to land the aircraft in a nearby clearing. The throttle was closed in an endeavour to reduce the fumes but reapplied when this was not successful. However, the engine did not respond and the aircraft was landed short of the cleared area. During the landing roll the aircraft collided with trees. Following the last engine start the starter relay contacts remained closed due to internal corrosion, this resulted in the motor continuing to operate. The continuous operation of the starter produced enough heat to melt the non-standard engine earth strap at the attachment point to the firewall. Earth was then made through the tachometer cable and magneto switch leads, which overheated and burnt causing the magnetos to earth and the engine to subsequently fail.
