Turning the red high-speed screw clockwise causes the carburetor to deliver less fuel and oil to the engine. Setting this screw too far clockwise will deprive the engine of lubricant, causing it to overheat. The proper setting for the high-speed screw allows the engine to run at full throttle smoothly without producing excessive amounts of smoke.
Always work on your tiller on a flat, stable surface and keep your hands and feet free of moving parts while the engine is running. Wear tight fitting clothing, tie back loose hair and remove any loose jewelry while working on a running motor. Choose a well-ventilated area to work in if you are performing a carburetor adjustment indoors.
Adjusting a rough, sputtering engine to produce the power you need helps propel a tiller's tines through even the hardest dirt clod. The Mantis tiller carburetors are adjusted using a red and a white screw located behind the air filter cover near the black choke button on the right side of the engine. The red screw adjusts the high-speed setting and the white screw controls the low-speed setting.
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Unscrew the wing nut sticking out from the center of the air filter cover and remove it from the bolt sticking out of the cover. Pull the cover off carefully so that it clears the choke button.
Check the air filter for dirt or damage, and replace it if necessary. Locate the red and white adjustment screws located beneath the primer bulb on the right side of the carburetor. The red screw is located to the left of the white screw.
Find the retaining pins at each end of the axle on which the cultivator's tines are mounted. Pull the long portion of each pin out until it clears the hole in each end of the axle; twist each pin out away from the axle to remove it. Slide the tines off the axle and set them aside.
Start the engine and allow it to run at idle speed for two to three minutes. Pull the choke button out briefly without allowing the engine to stall. This helps purge air from the fuel system while the engine is warming up.
Stop the engine and turn the red screw counterclockwise until it stops. Turn the white screw counterclockwise until it stops or is about to come out of the carburetor. Turn the white screw clockwise and take note of how many turns it takes for the screw to stop turning. Turn the white screw counterclockwise half as many turns as you counted; the white screw should be set half way between fully screwed in and out.
Restart the engine and run it at full throttle for two to three seconds, and then return the throttle to idle. Rev the engine at full throttle briefly and observe how it transitions from low to high speed. If the engine accelerates slowly, sputters or sounds rough, turn the white screw one-eighth of a turn counterclockwise and rev the engine again. Continue adjusting the white screw incrementally until the engine runs smoothly at idle and full throttle.