The idle jet is installed under the jet cover on the Weber DCOE series and 45 MCHH carburetors. The F designation indicates that this jet controls both air (side inlet hole) and fuel (inlet hole at the tip). The F number refers to air control, and the size number refers to fuel flow. Two idle jets are required per carburetor (one for MCHH). Sold individually.
Note that Weber assigned F numbers chronologically, as they designed the jets. They do not follow a linear "richest to leanest" sequence. The F6 allows air in through a single 0.70mm side bleed hole, making it the richest family of idle jets. The size numbers do follow a linear sequence, with larger numbers allowing a richer idle mixture. When switching from one F number to another, experts recommend starting with the same fuel size number.*
DCOE idle jets, listed in order from richest to leanest air bleed:
F6 DCOE Idle Jet (Part No. 74819, this jet): Single 0.70mm air bleed
F9 DCOE Idle Jet (Part No. 74822): Single 1.00mm air bleed
F8 DCOE Idle Jet (Part No. 74821): Single 1.20mm air bleed (large fuel bore)
F11 DCOE Idle Jet (Part No. 74824): Single 1.20mm air bleed (smaller fuel bore)
* If you need to go up one fuel size number, start over with an F11 idle jet. For example, if 45F6 is not rich enough, the next step richer would be 50F11.
Note: Fits genuine Weber (made in Italy or made in Spain) carburetors only! Does not fit most copies, Asian knock-offs, or work-alikes.