This article covers the selection and use of the Mercury 7824 Needle & Seat Kit for WH-series carburetors on Mercury/Mariner V6 two-stroke outboards. It targets buyers building or servicing 2.0L, 2.4L, and popular 2.5L conversions, including Black Max, XR2, XR4, SST-120, and SST-140. SEO focus: Mercury 7824 needle and seat kit, Mercury WH carb, V6 outboard carburetor parts, install, and float height adjustment.
Application and compatibility
The 7824 kit fits Mercury WH carburetors used across 2.0/2.4-liter V6 engines and many 2.5-liter performance builds. Confirm a “WH-xx” stamp on the carb body. For catalog searches, common equivalents include 18-7233, 40900, 509052, 6033, 7824B, 7824B1. If you’re running Mercury/Mariner 135, 150, 175, 200, 225 HP—including XR2/XR4/Black Max/SST-120/SST-140—this is the typical WH-spec needle & seat.
Quantity planning
Each WH carb requires two assemblies. A three-carb V6 needs six kits per engine; twin engines need twelve. Order one extra pair for bench spares during tuning.
What’s in the 7824 kit
You get a Viton-tipped needle, a threaded brass seat, a sealing washer, and often a needle clip. The kit restores precise bowl fuel level for stable idle, clean transition, and consistent WOT—core to Mercury WH carb tuning.
How to verify fit before installation
Open one carb and compare parts. The original seat should seal with a separate washer (not an integral O-ring). Match the seat head style/depth and confirm your float either clips the needle or pushes it cleanly. If these align, the Mercury 7824 needle and seat is correct.
Installation overview (best practice)
Work surgically clean. Flush passages with fresh carb cleaner and gentle air. Set the washer squarely, thread the seat by hand, and tighten lightly—sealing comes from the washer, not torque. Hang the needle if your float uses a clip, reinstall the float/pin, and verify free movement.
Setting float height the reliable way
With the bowl gasket removed, invert the carb and tilt it until the needle just touches the seat without compressing the spring tip. Set the float top 1/16" below, parallel to the bowl surface at this point. Return upright and confirm that the float drop is adequate. This method transfers across WH variants when a dimension isn’t published.
Bench check and on-water validation
Prime the system level. A primer bulb that goes firm and stays firm indicates proper seating; any softening, odor, or dampness signals a leak to fix before launch. On the water, warm fully, set baseline idle mixtures, and verify a crisp idle-to-plane transition. Rich stumble suggests high float level or float contact; a flat lean spot suggests low level or limited drop.
Troubleshooting after install
Flooding usually means the float was set with the spring compressed instead of at just-touch, or debris reached the seat. High-load starvation points to insufficient drop, restricted inlet screens, anti-siphon valves, or hose kinks. A new weep after refueling often indicates tank debris or hose liner shed, not a bad kit.
Maintenance notes
E10 fuel punishes idle bowls during storage. Stabilize fuel, keep a 10-micron water-separating filter fresh, and treat needle/seat service as periodic maintenance. Replace any heavy or fuel-soaked float; a bad float defeats perfect 7824 parts.
You’re buying the Mercury 7824 WH Carb Needle & Seat Kit. Two kits are required per carburetor; a three-carb V6 uses six per engine. Confirm WH-series stamping, cross-check with 18-7233/40900/509052/6033/7824B/7824B1, install cleanly, set float height by the just-touch method, and enjoy stable idle, sharp holeshot, and repeatable top-end on your Mercury/Mariner V6.
Billet Cover Plates and replacement Linkage is also available on this website.
Feel free to contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com for racer-level experience and the best technical support.