4. Setting up the Throttle Linkage:
This actually applies to any engine make. Use a good quality servo with no backlash or slop. Use a solid linkage between the servo and engine throttle arm - no floppy wires or plastic linkages - and make sure the friction is minimal. This is particularly important for getting a reliable fixed low idle position.
The following only applies if you have a computer radio that may be used for servo end-point adjustments to help set up the throttle throws.
First make the mechanical linkages such that the servo moves the throttle arm from approximate idle position to approximate full throttle position.
Next set the transmitter throttle trim lever to its center position (assuming you have a tranmitter with a mechanical trim lever and not electronic trim). Now move the transmitter stick to full throttle position.
Next look into the engine carb and you should see the carb barrel approximately fully open. Now, using the transmitter programming, adjust the servo end point adjustment back and forth while looking down the
carb - you want the servo end point adjustment set so that the carb just opens fully with the transmitter stick at the full throttle position - if it is not fully open you won’t get full power, and if the
servo is pushing too hard you will get high servo current drain when at full throttle.
Next move the transmitter stick to full idle position. The transmitter trim lever is still at its center position. Now adjust the low-throttle servo end point using the transmitter programming function so that
the carb opening is about 1/2 mm (this is a good starting point).
Start the engine, keeping the throttle trim lever centered and the transmitter stick a couple of clicks above its full idle position. Assuming you have already adjusted the carb needles for optimum running, the
low speed idle setting is set using the transmitter end-point adjustment, and not the throttle trim lever that stays centered. With this procedure you always know that a centered trim lever corresponds to the
correct idle rpm. For future changes to idle rpm that may be required always adjust the servo end-point adjustment using the computer programing function and not the trim lever position.
Remember, when starting the engine for the first flight of the day the engine will probably not maintain the same lowest idle rpm as the last time you flew. The first flight of the day is usually needed to
loosen up the engine. So don’t be tempted to adjust the idle rpm with the computer end-point adjustment until you have flown a flight or two. On the first flight of the day move the mechanical trim forward
a couple of clicks and then back to center for landing and subsequent flights.
Having a reliable and lowest-possible idle rpm helps with landing a model. You always know that setting the trim lever to center will provide that lowest idle rpm. If you are paranoid about avoiding engine
stoppages during a flight you can always take off with the trim lever a couple of clicks above its center position, then return it to center just before landing (this is a good procedure for a new engine).
[If you unfortunately own one of those transmitters with an electronic trim on the throttle you will need to adopt a somewhat different procedure from that outlined above]