How to Adjust the Mixing Screw on a TS125

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The Suzuki TS125 two-stroke, enduro-style motorbike incorporates a Mikuni VM carburettor that if tuned incorrectly will prevent the bike from performing at its optimum level. The carburettor manages the fuel air mixture before it is combusted in the single-cylinder engine.

Setting the fuel air mixture to as close to 1-to-15 as possible is done by the adjustment of the air screw on the casing of the carburettor.

Locate the air mixture screw on the carburettor. This can be found on the left-hand side of the bike, just under the intake manifold where the carburettor meets the engine. It is mounted diagonally facing downward. Do not confuse this screw with the idle mixture screw on the right side mounted horizontally.

Screw in the mixture screw clockwise until it stops. Do not apply force to the screw as doing so can damage the needle, or threads.

Turn the air mixture screw counterclockwise one full turn.

Start the bike and let it idle.

Turn the screw in clockwise until the rpm drop and it sounds as though it is going to stall.

Turn the screw counterclockwise until the rpm increase or the engine begins running worse. Be sure to count the number of turns made to find this point.

Turn the screw back in clockwise to the halfway point between the two settings. To find this point divide the number of turns made counterclockwise by two.