At low revs the throttle is basically closed and air is drawn through a small supplementary air passage with a small jet. The needle jet is mounted onto the slide.įuel is allowed into the air from various jets.
When you open the throttle the slide is lifted up, opening to allow more air into the engine. The slide is attached to the throttle cable. This means that there is lower pressure in the carb throttle than there is in the float bowl (which is just at normal air pressure) and so fuel is drawn up into the air. This narrowing causes the air to speed up at that point, which results in a drop in pressure.
The Dellorto PHBH28 carb is used on the NSR125 and variations of the same carb are also used on the Aprilia RS125 and the Cagiva Mito.Ī carb work by, in simple terms, creating a narrowing of the air passage.
