Most people who endeavor to work on or rebuild their own carburetors ignore the air bleeds. Every self-atomizing circuit has an air bleed. That is, every circuit designed to froth its fuel as it discharges, for the optimum combustion by the engine, has lateral holes in the jet that mix air into the fuel as it rises so it is atomized. The air bleed is important. It is just as critical as the fuel side of the passage, yet it is often forgotten, resulting in less than successful carburetor work. On variable venturi carburetors, the air bleeds are found on the air side of the carburetor body. Most constant velocity carburetors on the other hand have them at the top of the carb body, under the vacuum chamber. The air bleed jet must be cleaned because, despite it being air-specific, it in fact is subject to contact with fuel and therefore varnishes up just as the fuel jet does.

A rather well-known aftemarket repair manual famously made the mistake of assuming that air bleeds are proportionately sized to their fuel jets. That is, that a larger jet has a larger air bleed and a smaller jet a smaller air bleed. But the reality is the air bleed's relation to its jet is inverse. The larger jets have the smallest air bleeds and the smaller jets have the largest air bleeds. Thus the carburetor's main jet circuit--the largest one in the carburetor--can easily malfunction because its air bleed is very small indeed and thus prone to blockage from fuel varnish. A simple poke and then aerosol spray can "wake up" a main circuit dramatically.

Honda's carburetor company, Keihin, traditionally has made the air bleed jet non-removable. In a very few instances they opted to manufacture carburetors with removable air bleed jets, mostly in carbs designed for racing, and famously, also in the earliest examples of the Gold Wing, the GL1000, whose design owes much to automotive engineering, which is probably why it got removable jets. But most are pressed-in and that is just fine on carbs that won't see high performance duty. Being permanently installed however means they tend to be overlooked, so don't. Flush them just as you do the fuel circuits.

For more on carburetors in general, check out my carburetor series.