How to Adjust the Carburetor on an Outboard Boat Motor

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Outboard motors are the "go to" motor for most boaters on the water, as they are easy to learn and relatively inexpensive to maintain. For the most part, outboards will perform day in and day out without requiring anything more than routine maintenance. However, there are times when, after running strong for a long time, the carburetor will begin causing problems with the idle speed or the performance of the motor. It is during these times that understanding how to adjust the carburetor is extremely useful.

Items you will need

  • Screwdriver Needle-nosed pliers

Start the motor and allow it to start idling. Find the idle adjustment screw, located on the lower half of the carburetor and the only screw with a spring on it, and turn it counterclockwise until the engine is just barely idling. Turn the valve screw (located on the left upper part of the carburetor) clockwise in 1/8th turn segments until you achieve a smooth, steady idle.

Slide the lower holder off of the bottom of the carburetor and slowly lower the carburetor bowl away from the carburetor. The holder looks like a thick wire that transects the bottom of the carburetor and the float bowl is the lower half of the carburetor housing where the excess gas sits. If you cannot get the motor to stay running or to idle, you may need to adjust your float bowl height. Improper gas levels can lead to a rough running engine.

Consult your owner's manual for the manufacturer's recommended float bowl height. Use the needle-nosed pliers to bend the float tab (located on the two brass "floats" inside the float bowl) to match the recommendation of the manufacturer. Reinstall the float bowl and then slide the wire holder onto the bottom of the carburetor float bowl. Start the motor and listen to see how smoothly it runs.


  • If your motor is running exceptionally rough or inconsistently, you may need to remove the carburetor and clean the needle valve (the valve that delivers gas to the intake). This is best done by a repair shop or an experienced mechanic.