Throttle slides can come in many shapes and sizes, but the two found most often in moped carburetors are the round slide and the flat slide. Round slides are found in Bing, Dellorto PHBG, and some Mikuni carburetors. Flat slides are found in Dellorto SHA and larger Mikuni carburetors. Round throttle slides also have an angled cutout on the side of the throttle slide facing the air filter. The degree of cutout can affect mixture from idle to the first 1/4 of throttle opening. Some throttle slides also have needles which hang in a vertical hole in the throttle slide.
How it works
In the fully closed position, the throttle slide is pushed to the bottom of the track it rides in by a spring which sits between the top of the throttle slide and the top of the carburetor. At the bottom of its track, it cuts off almost all of the airflow through the venturi, or "throat" of the carburetor, allowing the engine to idle. A cable is attached to the throttle slide, and when that cable is pulled, the throttle slide moves upward, opening up more of the venturi and allowing air to flow through and mix with fuel. When the throttle slide is raised to its highest possible position, it uncovers the entire venturi of the carburetor, allowing for maximum air flow. At this point, the carburetor is "wide open," and often reference will be made to how an engine performs at WOT, or Wide Open Throttle position.