Publicatin
JP OM15
Jabiru J400
Owners Manual
Section: 3
3.4.
OTHER PROCEDURES
3.4.1. CARBURETTOR HEAT
This system serves to prevent the formation of ice within the carburettor, where it
primarily forms on the throttle plates in such a manner as to obstruct the airflow, with
resultant eventual engine stoppage. Vaporisation of the fuel & expansion of air
through the carburettor cause a cooling of the mixture, which can be as much as 15
degrees C below the temperature of the ambient air. This permits moisture in the air
to condense and form ice. The first indications of icing are an RPM drop or a drop in
manifold pressure. Progressive icing will cause obstruction of the carburettor, which
manifests itself in the form of a rough running engine. During this time the smaller
volume of air aspirated has richened the mixture. Ice can form more rapidly with
partial throttle, due to the lower pressure in the carburettor. At full throttle, the
danger is lessened somewhat. Therefore, carburettor heat is not to be used during
takeoff or climb, also because it creates a small power loss.
IMPORTANT
During descent & approach, the carburettor heat should be used because low power
settings create low pressures in the induction manifold. In case of a go-around, turn
the carburettor heat OFF. Prolonged use of carburettor heat with more than 80%
power applied could provoke detonation.
When using Carburettor Heat, pull knob to FULL ON.
DO NOT use partial Carburettor Heat.
Carburetor icing can occur when on the ground, particularly when the aircraft and
engine have become damp overnight. Check carburetor heat during power check as
normal, prior to lining up on runway close the throttle completely, if a low tick over or
engine stoppage occurs ice is present so burn it off with twenty seconds of heat and
then test again prior to take off.
3.4.2. IGNITION MALFUNCTION
A sudden engine roughness or misfiring is usually evidence of ignition problems.
Switching from both ON to alternately switching each system OFF will identify which
system is malfunctioning. Switch to the good system and proceed to the nearest
airport for repairs.
REVISION
0
Date SEPT 00
Page 3-11 of 11
