Air bleed jets

[mikenixon]

A carburetor circuit that atomizes (as opposed to a non-atomizing circuit) does so by having air spiked into its fuel by atmospheric pressure. 1 That is, the circuit has paths that acquire air as well as fuel and the two are mixed before discharging into the carburetor. The air path of this arrangement is known as the "air bleed", a term also applied to compressed air paint guns. Because carburetors are manufactured to fit more than one year model and for use in more than one sales area, their passages are made slightly oversize and then sized down from there for specific application by "jets". The jets are not themselves the passages, they are the gatekeepers to the passages. Jets are found on air bleed passages (in racing they're called "correction" jets) as well as on fuel passages. Or as mechanics like to say, "circuits".

On the majority of streetbike carburetors, the fuel jets are removable but the air bleed jets are not. 2 The GL1000 is unique among production carburetors however in having removable air bleed jets, probably a holdover from the carburetor's origin in the Honda 600cc car.

The GL1000 has twelve air bleed jets, three in each carburetor. One each for the carb's idle, primary main and secondary main circuits. One of the most common things rebuilders-- whether pro or DIY-- have to deal with is GL1000 air bleed jets that are installed in the wrong places and in many cases even unnumbered, the latter indicating kit parts. Although Honda specified different size air bleed jets for the several models of GL1000 carburetors, carb rebuild kits often do not meet the challenge of having the right ones for the model in question, and as already mentioned, they are sometimes not even marked, making things doubly challenging. Those who rebuild GL1000 carbs have to have jet sizing tools on hand as well as spare air bleed jets in order to do a quality job. Replacement air bleed jets are obtainable from a few sources, among them JetsRUs.com.

Make sure you are not tripped up by the non-intuitive placement of the GL1000's primary main and secondary main air bleed jets. The smaller jet goes into the larger, secondary main circuit while the larger jet goes into the smaller, primary main circuit. While seemingly peculiar, this is standard practice on Japanese carburetors.

1 A non-atomizing circuit is one that does not aerate, that is, does not atomize, until it reaches the carburetor's moving airstream. The accelerator pump is an example. Almost all other circuits pre-atomize before atomizing a second time upon discharge.

2 In production motorcycle carburetors, removable air bleed jets are unusual. They are typically found only in racing carburetors, where they exist to provide another layer of tuneability.