A: The Low-Speed Needle: The low speed needle of the M-39x carburetor is hidden in the center of the carburetor barrel. You need to use a small precision flat blade screwdriver to adjust it. When adjusting the Low-Speed Needle, apply Loctite#222 on the needle thread in order to hold the needle in position during operation.

The Low-Speed Needle is set at 7 turns out from fully closed (or fully screwed in).

B: High-Speed Needle: The High-Speed Needle is set approximately 2 turns out from fully closed.

C: Idle Screw: Set this at the lowest RPM where the engine idles reliable without stopping. Screwing the idle screw in will make your engine rev faster.

Setting Your Throttle Servo

Arrow Shark X-30 and X-60 Marine engine was designed with intergrated throttle servo control kit which directly link to M-39X carburetor with ball joint tie-rod for the most easy and effective operation, but you still need to adjust the radio setting for your throttle servo to function properly. so that the engine idles smoothly when your radio transmitter trigger (or other throttle control if not a wheel/trigger transmitter) is at its neutral position. You may need to adjust the throttle pushrod linkage and/or use your throttle trim to adjust the idle speed up or down to get a reliable idle. When your trigger is pulled fully open for high speed, the servo movement should have the engine’s throttle barrel fully open. You may need to adjust your pushrod linkage and/or the servo’s travel so that the throttle barrel is fully open with the trigger pulled all the way, but the servo should not stall by trying to force the barrel further than it will go. Finally, the servo should be adjusted so that it fully closes the barrel and stops the engine when you push the trigger.

Your radio should also be equipped with a “Fail Safe” system which closes the throttle in the event of radio failure or loss of signal. If this is not an integral facility within your radio, you will need to fit a separate Fail Safe – these are readily available from good hobby stores. Follow the radio or Fail Safe instructions and set it so that the M-39X barrel is fully closed when your transmitter is turned off.

M-39X Adjusting Tips

When adjusting the needles from their standard settings, move them only 1/8 of a turn a time. Check the results then adjust further as needed. Never attempt to tune the high-speed needle by running the engine at full throttle out of the water! This is very dangerous and damages the engine. The following tips may assist in setting your M-39X Carburetor for optimum engine performance.