3. Pinch the fuel intake line between your fingers to restrict fuel
flow, while listening to the engine rpm. If the rpm increases
immediately, this may indicate that the low speed needle
valve is set too lean. Richen as necessary. Adjust the low
speed needle valve until a reliable idle is achieved and a hesi-
tation of 2–3 seconds is established once the fuel line is
pinched.
4. Test hover the helicopter by advancing the transmitter throt-
tle stick gradually until the helicopter just lifts up (floats)
from the ground. Warm up the engine while maintaining a
low level floating hover for approximately 10 seconds, then
slowly reduce the engine speed and allow the engine to idle
for a while. If the engine remains at a high idle for a few
seconds, then settles down (loses rpm), this may indicate
that the engine is running too lean. Adjust the low speed
needle valve in small 1/8 turn increments until the engine
will return to a low idle directly after hovering.
5. Repeat the above procedure several times. If the engine tends
to hesitate or cut-out as the throttle is increased, this may
indicate that the low (or high) speed needle valve is set too
rich. Lean the low speed needle valve slightly and re-test
until an acceptable throttle response is achieved. On the
contrary, if the low speed needle valve is set too lean, the
engine may hesitate longer and exhibit a weaker exhaust
tone. It may also be possible that the engine will run roughly
and produce a “missing” or inconsistent exhaust sound.
Richen the low speed needle valve as needed until the proper
adjustment is achieved.
6. If the engine runs with hesitation but does not stop, try to
hover the helicopter, maintaining an altitude of approxi-
mately 1 foot from the ground and carefully watching the
exhaust smoke. If the mixture is too rich, you may observe
an excess of exhaust smoke and the throttle response will be
very soft. If the mixture is too lean, the engine will run with
a higher pitched exhaust sound, lose power gradually, and
little smoke will be produced, showing an overheating ten-
dency. It will be difficult to maintain a hover or keep the
helicopter flying. CAUTION: Do not continue to fly the
helicopter in this condition as this could cause severe dam-
age to your engine. Re-adjust the fuel mixture as needed.
Note: In most cases, the higher the nitro content of the fuel,
the more the engine will smoke due to increased oil content
in the fuel.
Maximizing High Speed Performance
This setting will depend on the individual characteristics of the
helicopter engine/muffler configuration, the fuel used, and the
atmospheric conditions. The high speed needle valve should be
gradually closed (leaned out) in 1/8 turn increments until the
highest performance is obtained in flight at full power.
CAUTION: Do not close the high speed needle valve to a lean
setting and risk overheating the engine during the first 6–8
tankfuls of operation during the initial break-in process.
Operating the engine at too lean a setting in pursuit of maxi-
mum performance is not recommended and can cause damage
to the engine. Note: Do not attempt these adjustments until a
reliable fuel mixture setting in the initial hovering position has
been achieved. If you are not proficient in forward flight, seek
the help of a more experienced pilot for these adjustments.
Maximizing Middle Range of Performance
(Hovering speed)
In helicopter flight, throttle response at hovering speeds is very
important. If the low speed needle valve and high speed needle
valve are properly adjusted (balanced) the mixture will be cor-
rect through the middle range of performance. If, however,
minor re-adjustments are necessary for the best possible throttle
response, use the following symptoms to make the necessary
corrections:
1. If the mixture at the middle range of operation is too lean,
gradually increased engine speed is accompanied by dimin-
ished exhaust smoke and a high-pitched exhaust sound
while maintaining a hover. In some extreme cases, the
engine will overheat and begin to lose power to a point
where a hover cannot be maintained. In this situation, open
both the high speed and low speed needles valve 1/8 turn
counterclockwise (richer) and retest.
2. If the mixture at middle range of operation is too rich, posi-
tive and quick throttle response will not be possible to
obtain. Exhaust smoke will be dense, and the exhaust sound
will be lower, accompanied sometimes by a considerably
reduced rotor speed. When this occurs, close both the high
speed and low speed needle valves clockwise (leaner) 1/8 of a
turn and re-test.
Note: Make any needle valve adjustments in small increments
of not more than 1/8 of a turn when trying to make adjust-
ments to the middle range of operation. Excessive re-adjust-
ment will upset either the low or high speed performance. Be
patient when making re-adjustments so you can find the best
balance of idle, hover and high speed performance. You want
the engine to respond quickly and positively to the throttle
control. Throttle response at hovering speeds is also affected by
the relationship of the main rotor pitch curves and engine
throttle curves. If the optimum middle range throttle response
cannot be obtained using the carburetor adjustments described
above, try adjusting the helicopter’s pitch and throttle curves to
achieve the desired response.
E. Engine Care
Dos
Fuel
Always use clean, fresh fuel. Because dirt is the number one
enemy of any engine, we highly recommend the use of an
in-line fuel filter between the tank and the carburetor. Also,
place one between your fuel pump and the tank filler line.
After-Run Oil
Because model fuel contains methanol, it has the property of
drawing moisture from the atmosphere. Exposure to moisture
can cause corrosion to such vital engine parts as the bearings
and crankshaft. Therefore, we strongly urge that after every
flying session you drain all fuel from the tank and then put
approximately 1 oz. of after-run fuel into the fuel tank. We
recommend Hangar 9 Final Run (HAN3100). Start the engine
and let it run for 1–2 minutes at idle. Drain the excess after-run
fuel from the tank. Your engine will now be protected against
corrosion.
Glow Plug
Proper glow plug selection is extremely important if you are to
achieve maximum performance from your MDS heli engine.
We recommend the use of the Hangar 9 #3 heli performance
plug (HAN3020).
Inspection
Periodically remove the muffler and inspect the piston
through the exhaust port. Any signs of scoring may be an
indication that the engine has been overheated and run in a
lean condition.
Don’ts
Don’t dismantle the engine unnecessarily as doing so can
cause damage to the precision fit parts, such as the piston and
sleeve. If it’s necessary to clean the interior of the engine (such
as after a crash), remove only the muffler, carburetor, cylinder
head and backplate. You should be able to clean all foreign
matter from the engine without disturbing the fit of the preci-
sion parts. Any further disassembly could result in voiding the
manufacturer’s warranty.
F. MDS Safety Instructions and Warnings
See the enclosed safety instruction card for details.
G. Service and Warranty
See the enclosed registration card for details.
