Idle air screw adjustment

idle air screw

Often forgotten, idle air screw is the third most important piece to control air/ fuel mixture in a Rotax Max carburettor. It’s responsible for the transition between mixture delivery from the idle circuit and the beginning of mixture delivery from the main jet circuit. So, its main role is when the driver starts to open the throttle.

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Carburetor icing

carb ice

Carburetor icing occurs when there is humid air, and the temperature drop in the venturi causes the water vapor to freeze. The ice will form on the surfaces of the carburetor throat, further restricting it. This may increase the Venturi effect initially, but eventually restricts airflow, perhaps even causing a complete blockage of the carburetor.

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How to change a main jet

Main Jet change

This article describes the appropiate procedure to change a main jet without spilling fuel and refilling of the float chamber for an immediately re-start of the engine.

This procedure can be applied for:

★ 125 Micro MAX

★ 125 Mini MAX

★ 125 Junior MAX

★ 125 MAX

★ 125 MAX DD2

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Rotax jetting theory

Dellorto carburetor

Carburetor's main function is to form a "proper" homogeneous inflammable mixture of fuel and air. This fuel-air mixture is formed through vapourising and by uniformly spraying fuel into the airstream or at least by atomising it into very small droplets.

In order to get this "proper" mixture of gas and air, several adjustments has to be taken into consideration, as venturi insert size, floats weight, floats height, needle, jets (main, idlle, chocke), etc.

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