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The chart provided below indicates what the standard size jet, metering rods and metering rod springs are for your particular carburetor. It is important to not rely on printed specifications, but instead watch how your spark plugs burn. Written specifications do not take into consideration the low quality of gasoline we are now being provided. Your spark plugs should burn with a gray color, black indicates too rich, white indicates too lean.

The Weber marine carburetor uses metering rods, 2 step and sometimes 3 step types to meter the amount of fuel going through the main jets at cruise and at power. At idle the vacuum is at it's highest, and the metering rod drops down allowing the biggest step in the rod to enter the main jet, restricting fuel. As you power up, vacuum falls and the metering rod pulls out of the main jet allowing more fuel to flow through the jet.

Metering rod springs are used with the metering rods to factilitate rod movement depending on vacuum.

Metering rods and metering rod springs can be changed out while the carburetor is on the engine. Always be careful not to drop any parts down the carburetor.

Each side of the carburetor has a primary and a secondary jet. The primary jet sits up slightly from the secondary and is nearest the primary throttle valves. The secondary jet is on the bottom of the bowl and near the secondary (bigger) throttle valves. See the illustration below. (a) primary, (b) secondary.

EngineCarburetor NumberPrimary JetSecondary JetMetering Rod #Metering Rod Spring
MCM 7.4L SN OF352105 & below3310-818659 9772S.107.09816-6542Pink
MCM 7.4L SN OF 352106 & above3310-806969 9780S.104.098* 16-757347Green/Plain
MCM 7.4L Bravo 3 SN OF070156 & above3310-818659 9772S.107.098 (port), .077 (starb)16-6542Pink
MCM 7.4L Bravo 3 SN OF070155 & below3310-805569 9777S.107.09816-7147Pink
MCM 7.4L3310-806969 9780S.104.098* 16-757347Green/Plain
MCM 454 Magnum SN OF304599 & below3310-816917 9773S.107.10716-6542Pink
MCM 454 Magnum SN OF305000 & above3310-806755 9779S.106.092* 16-757347Green/Plain
MCM 502 Magnum 3310-805341 9776S, 3310-806791 9776S.110.10116-7147Pink
MIE 7.4L Bluewater3310-818659 9772S.107.098 (port), .077 (starb)16-6542Pink
3310-806969 9780S.104.098* 16-757347Green/Plain
MIE 8.2L Bluewater3310-817693 9774S.104 (port), .107 (starboard).09816-6542Pink
MIE 8.2L Bluewater3310-805341 9776S, 3310-805341 9776SA, 3310-806971 9776SB.110.10116-7147Pink

* These are 3 step metering rods, others are 2 step. 3 step metering rods use different main jets than the 2 step.
Your carburetor may have stagered sizes from side to side. Replace with the size above.

Elevations above 5,000 ft. reduce your seconday jet by 2 sizes.

Pink - 7 HG
Green/Plain - 8 HG

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