How to Adjust a Carburetor on Other Vehiclesby Contributing Writer; Updated June 12, 2017
To this end, the ATV's carburetor can be adjusted to via two screws; one screw sets the engine's idle speed, while the second screw regulates the air and fuel mixture used by the engine from idle to a quarter-throttle. Carburetor adjustments should be made immediately after the carburetor has been disassembled or if the engine will not hold a steady idle.
Under The Hood:
Start the engine and allow the ATV to run for five minutes.
Shut the engine off and locate the carburetor assembly directly beneath the fuel tank and the finned portion of the engine cylinder. The carburetor connects to the engine's intake manifold and features a large round shaped cap mounted on top.
Tighten the carburetor’s brass-colored mixture adjustment screw clockwise until fully tightened. The mixture adjustment screw resides next to the air filter box inlet connection, left of center, visible from the right side of the vehicle.
Turn the mixture adjustment screw counterclockwise, two full turns.
Start the engine and adjust the idle speed screw until the engine steadily idles between 1,500 and 1,600 RPM. The idle adjustment screw resides directly below the round cap on the center of the carburetor assembly.
Turn the mixture adjustment screw both clockwise and counterclockwise in a slow manner, until the engine idle reaches its maximum. Readjust the idle adjustment screw until the engine idles back down between 1,500 and 1,600 RPM.
Repeat the previous step to fine-tune the carburetor. Shut off the engine after completing the final adjustments.
Items you will need
Small flat-head screwdriver
Park the ATV on a flat, level work surface and set the parking brake.
Reach under the right front fender and grasp the spark plug wire protruding from the front of the engine cylinder head cover. Clamp an inductive tachometer onto the spark plug wire.
Unlock the seat, using the release lever under the left side of the seat, then remove the seat from the ATV. Pull the recoil starter cover, the panel located directly below the right side of the seat between the front and rear fenders, off of the ATV by hand.
Turn on the inductive tachometer. Start the engine and let it idle in place for three to five minutes to allow the engine to warm to its operating temperature. Do not make any adjustments or measurements until the engine has warmed thoroughly.
Take note of the engine's idle speed displayed on the tachometer. Ideally, the engine should be idling steadily within a 100 rpm range of 1,400 rpm once warm.
Twist the black idle adjustment knob, located on the right side of the carburetor counterclockwise by hand to reduce the idle speed, or clockwise to increase the idle speed. Stop when the engine is idling at 1,400 rpm.
Turn the pilot screw, located directly at the bottom of the carburetor directly under the engine's intake flange, clockwise a quarter-turn at a time with a D-Type pilot screw wrench (Honda part no. 07KMA-MN9A100). Stop when the idle speed begins to rise slightly. Alternatively, if the idle speed does not rise after one full turn, turn the pilot screw counterclockwise a full turn, then continue to turn the screw counterclockwise a quarter-turn at a time. Stop when the idle speed begins to rise slightly.
Reset the engine idle speed to 1,400 rpm, then stop the engine.
Disconnect the tachometer from the spark plug wire. Push the recoil starter cover onto the frame until the mounting bosses molded into the rear of the cover are seated firmly in the rubber grommets along the ATV's frame. Re-install the seat onto the ATV.
Items you will need
D-Type pilot screw wrench (Honda part no. 07KMA-MN9A100)