5. In many helicopter installations, it will be necessary to
replace the existing throttle arm with the extended heli
throttle arm provided in the parts bag (.38 & .48 only). In
most cases, it’s suggested that the throttle arm be positioned
once the engine has been installed in the helicopter to
achieve proper alignment and to accomodate each engine
installation. Prior to attaching the throttle arm, it’s also
suggested that you first test fit the desired control linkage to
the throttle arm to insure that the attachment holes in the
throttle arm are of the correct size. In some cases, it may be
necessary to enlarge the attachment holes using a drill for
proper fit. Note: The holes are already enlarged in the .68
heli engine.
6. Attach the appropriate fan/flywheel assembly included with
your helicopter kit per the kit manufacturer’s instructions. A
tapered collet and knurled prop washer, as well as a stepped
spacer, have been included with this engine to facilitate
fan/flywheel assemblies which require this arrangement
(.38 & .48 engines only). If the tapered collet/knurled
prop washer are to be used, it will first be necessary to
remove the stepped spacer from the engine prior to attache-
ment. Note: When attaching and tightening the fan/fly-
wheel assembly to the engine, it’s suggested that a piston
locking tool be used to achieve proper tightness. We recom-
mend the Revolution Piston Locking Tool (RVO1003) or sim-
ilar item.
7. Install the engine into the helicopter per the kit manufac-
turer’s recommendations.
B. Understanding Your MDS Aeromix
™
Carburetor
The MDS Aeromix
™
carburetor is designed for use with the
Pro series of MDS helicopter engines. This carburetor provides
the proper air-fuel mixture necessary for helicopter flying and
provides smooth performance throughout the throttle operat-
ing range.
Note: If this is your first attempt at operating a model engine,
we suggest you seek the advice of an experienced modeler for
help, if possible. Your local hobby dealer may be able to help or
put you in contact with an experienced modeler who would be
willing to help you.
CAUTION: Before making any adjustments to the carburetor,
please consider the following: In helicopters, engine failure in
flight is a serious problem, especially for modelers who do not
have much flying experience. Such a failure will usually result
in loss of control of the helicopter and a resulting crash.
To ensure safe, reliable control of the helicopter in flight, you
must adjust the engine to achieve a throttle response that’s
quick and reliable. This means the carburetor adjustment is
very important for proper helicopter performance and must be
done with great care in order to obtain reliable throttle
response. Initial test flights are recommended at a very low
altitude (approximately 1 foot or less from the ground) until
reliable operation is achieved.
When the helicopter is in flight, accurate and reliable throttle
response in the medium speed hover range is very important!
This is because most initial helicopter flying (hovering) is done
at the medium speed position.
On this carburetor, there are two adjustable needle valves for
fuel flow control.
High Speed Needle Valve
1. The High Speed Needle Valve (located on the left side of
carburetor as you look at the engine from the rear forward)
controls the mixture of the engine speed range from half
(midstick) to fully opened throttle.
Low Speed Needle Valve
2. Low (idle) Speed Needle Valve (located in the throttle barrel
in right side with throttle arm) controls the mixture of
the engine speed range from idling to half open throttle
(midstick). Note: The idle needle valve is recessed into the
throttle arm extension on the .68 heli engines.
Note that the best mixture around half (midstick) throttle is
obtained by balancing the High Speed Needle Valve and the
Low Speed Needle Valve Settings.
Suggested Initial Needle Valve Settings:
High Speed Needle Valve: 2-1/2 turns
Low Speed Needle Valve: 2-1/2 turns
Please note that all settings are established by turning the
respective needle valve clockwise until it stops, then backing
out counterclockwise to the desired position.
C. Engine Break-in
Your new MDS helicopter engine can be broken-in either in the
helicopter or on an engine test stand. Most helicopter pilots
choose to break-in their new engines while in the helicopter.
This is an acceptable practice, provided that the engine is run
in a low rpm condition, with a rich needle setting for a mini-
mum of 6 –8 tanks of fuel. Once this has been completed, the
engine can be leaned down in small increments and taken to
full power as needed. Note: If the engine is used in a lean or
full power condition during the first 6 –8 flights, possible dam-
age can occur, voiding the warranty.
D. Initial Test Flights and Adjustments
To start the engine, you will need the following items:
• We recommend a high quality, 2-cycle heli fuel
containing 15% to 30% nitromethane.
• Fuel pump
• Electric starter with appropriate extension
• Glow driver or power panel
• Glow plug (HAN3020 recommended)
• In-line fuel filter
The following adjustment procedures are recommended:
Initial Carburetor Adjustments
(Range from idle to 1/2 open throttle)
1. Start the engine with the transmitter throttle stick fully
down and the throttle trim lever set in the center position.
Be sure to hold the rotor blades firmly while starting in case
of clutch engagement.
2. Set the throttle trim lever so the engine runs with the high-
est idling rpm possible, without engaging the clutch. Let the
engine run for 1–2 minutes in this condition to warm up.
Photo 3
Carburetor barrel fully closed
Idle stop screw
Photo 4
Low Speed
Needle Valve
recessed inside
(.68 only)
High Speed
Needle Valve
Throttle Arm Extension
(.68 only)
