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Running-in(“Breaking-in”)
All internal-combustion engines benefit, to some degree, from extra care when they are run for the first few times known as running-in or breaking-in.
This allows the working parts to mate together under load at operating temperature.
However, because the engine are made with the aid of the finest modern precision machinely and from the best and most suitable materials, only a very short and simple running-in procedure is required and can be carried out with the engine installed in the model.
For the first few flights with a new engine i.e. while the engine is being run-in set the needle-valve for a slightly rich mixture not excessively rich as this may result in poor throttle response and cause the engine to stop.
About one half turn open from the Normal setting will usually suffice.
ADJUSTMENT
Please observe the following before beginning to make any adjustment.
1) High-Speed Needle Valve. Turn this approximately 30 degrees (3 to 4 clicks) at a time, when making initial adjustments; then in steps of approximately 15 degrees (1 to 2 clicks) when making final adjustments.
2) Medium-Speed Needle Valve. Turn approximately 30 degrees (3 to 4 clicks) at a time.
3) Idle Mixture Control Screw. Turn approximately 5 degrees at a time. It turns approximately 90 degrees both sides from the center. Turn left to enrich the idle mixture and turn right to lean the idle mixture.
The general course of adjustment procedure is shown in the ADJUSTING CHART and is correct for a fuel containing 20% lubricant and 15-30%nitromethane.
Bear in mind that fuels containing relatively large percentages of power-boosting nitro-methane operate at richer mixture settings that are needed for mild fuels and will, therefore, require the High-Speed Needle Valve to be readjusted accordingly. The type and percentage of lubricant used is also a factor here, as noted later in these instructions.
This carburetor is not equipped with a throttle stop screw. Instead, idle speed is adjusted by means of the throttle trim lever on the transmitter.
ADJUSTMENT PROCEDURE
As a safety measure, first check the transmitter controls, including the throttle stick and trim lever positions, and hold the main rotor securely before starting the engine.
1. Warm the engine by allowing it to idle for about 30 seconds. If the engine stops, advance the throttle trim lever slightly to increase the idle rpm.
Then open the throttle sufficiently to ‘float’ the model above the ground. If, at this time, the engine is slow to pick up and produces and excess of exhaust smoke, the mixture is too rich.
Correct this condition by turning the Mixture Control Screw clockwise 5 degrees. If the mixture is extremely rich, engine rpm will become unstable: opening the throttle will produce a great deal of smoke and rpm may drop suddenly or the engine may stop.
This condition may also be initiated by an excessively prolonged warming-up period. If, on the other hand, the mixture is too lean, this will be indicated by a marked lack of exhaust smoke and a tendency for the engine to cut out when the throttle is opened. In this case, turn the Mixture Control Screw counter-clockwise 5 degrees to enrich the mixture.
2. Having provisionally set the idle mixture, the next step is to adjust the mixture for hovering flight.
Hover the model and actuate the throttle to observe response over the medium speed range. If the engine smokes excessively and throttle response is poor, the mixture is too rich; in which case, land the model and turn the High-Speed Needle Valve clockwise. Do not close the High-Speed Needle Valve more than the recommended initial adjustment(3 to 4 clicks) at a time, keeping it a little on the rich side at this stage. DO NOT touch the Medium Speed Needle Valve.
If, on the other hand, hovering is not stable and response to the throttle is over-sensitive, or if the engine tends to overheat, this indicates that the mixture is too lean and should be corrected by turning the High-Speed Needle Valve counter-clockwise.
When satisfactory hovering flight has been achieved, land the model again and re-check the engine’s idle qualities.
After about 10 seconds of idling, open the throttle to ‘float’ the model. If the transition is smooth, the idle mixture is OK. If the symptoms of either rich or lean running are observed, readjust the Idle Mixture Control Screw accordingly.
NOTE: With this carburetor, neither the Idle Mixture Control Screw adjustment, nor the Medium Speed Needle Valve adjustment will have any effect on mixture strength when the throttle is fully(or almost fully) open.
3. Now adjust the High-Speed Needle Valve to achieve the best performance when the model is flying at full throttle. If, at full throttle, acceleration is poor, the exhaust unduly smoky and the model fails to reach expected straight line speed, the mixture is too rich and the High-Speed Needle Valve setting will need to be reduced.
If, however, after smoothly accelerating to satisfactory high-speed straight and level flight, power is lost when the model is pulled up into a climb, the mixture is too lean. In this case, land the model immediately and readjust the High-Speed Needle Valve to a richer setting.
4. Having now found the optimum setting for the High-Speed Needle Valve, re-check the engine’s idle performance, fine tuning the Idle Mixture Control Screw, if necessary, to perfect the idle.
5. Now re-check hovering performance it may be found that (with the High-Speed Needle Valve now set for optimum full-throttle performance) hovering will reveal symptoms of slightly lean running at medium speeds. DO NOT touch the High-Speed Needle Valve.
It is at this point that the Medium Speed Needle Valve, previously set two turns open, may be brought into operation. Open the Medium Speed Needle Valve 30 degrees, or 3-4 clicks, then fine tune until the optimum hovering performance is obtained. If, on the other hand, hovering reveals rich running, close the Medium Speed Needle Valve gradually until the optimum hovering performance is obtained. |
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