Two mixture controls are available on the carburetor.
1 Needle Valve
To our radio controlled plane we love to have nitro engine as the power unit for our model plane since it gives great sound and power in the air. After the breaking-in period is over we have set the needle valve so that it optimizes the engine running power. When set to produce maximum at full throttle this established the basic fuel/air mixture strength. The correct mixture is then maintained by the carburetor’s built-in automatic mixture control system to cover the engine’s requirements .
2 Mixture Control Valve
This is the fine tune element of the engine that meters fuel flow at part-throttle and idling speeds to that the engine runs on reliable operation as the throttle is opened and closed. The mixture control valve is factory set for the approximate best results. First run the engine as received and readjust the mixture control screw only if necessary.
Mixture control valve of the carburetor is set at basic position (a little on rich side) at the factory. During the running-in period of your radio controlled plane the flight should be made with slightly rich needle setting. Therefore during the running-in period proper carburetor response will not be obtained. However after the running-in is completed a minor readjustment will be required to reach an optimum position. You can also adjust the mixture control valve according to atmospheric conditions and fuel selection on a model.
Mixture Control Valve Adjustment
With the engine running, close the throttle and allow it to idle about five seconds, then open the throttle fully. At this point if the engine is slow to pick up and produces an excessive smoke, the mixture is too rich. Correct this condition by turning the Mixture control screw clockwise 15-30 degrees. If the mixture is excessively rich the engine rpm will become unstable: open 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 excessively prolonged idling.
If, on the other hand, the mixture is too lean, this will be indicated by a marked lack of exhaust smoke and a tendency of engine to cut out when the throttle is open. In this case, turn the Mixture Control Screw counter-clockwise 90 degrees to positively enrich the idle mixture, then turn the screw clockwise gradually until the engine regains full power cleanly when the throttle is reopened. Carry out adjustments patiently until the engine responds quickly and positively to the throttle control.
Note: Mixture control valve adjustments should be made in steps of 15-30 degree initially, carefully checking the effect on throttle response of each small adjustment.