The zinc alloy throttle slide is a direct replacement for the original Amal 900 series Concentric carburetors. The size of the cutaway has an atmospheric influence on the transition between the pilot circuit and the initial main circuitry fuel feeding through the needle jet at off-idle and lower throttle positions. A worn throttle slide will have a negative effect on performance of the carburetor.
The genuine Amal 3.0 cutaway throttle slide is precision manufactured in the UK. The amount of throttle slide cutaway is designated in 1/16″ for each full increment. Ordinarily, the 3.0 cutaway is specified for twin cylinder engines with dual carburetor cylinder heads, such as the BSA Lightning, Norton 750 Commando, and Triumph T120 and T140 Bonneville models.
The slide is not only is used for fine tuning low throttle positions, but also houses the jet needle, lifting it out of the needle jet when the throttle is opened. The lower the number of the cutaway indicates a smaller cutaway and will give a richer fuel charge at off-idle position, up to approximately 1/4 throttle, when the needle position within the needle jet has a greater influence on the fuel mixture as engine speed increases. There is a separate column in the front of the slide for the choke block, which is operated independently of the throttle slide.
The top cap must be removed from the carburetor’s mixing chamber and the throttle slide assembly withdrawn. The slide return spring must be compressed to allow the needle and throttle cable to be removed. Once the slide has been refitted, the carburetor will likely require adjustment to optimize performance.