On legacy Mercury 2-stroke performance outboards, the small brass “bleed line” check valves do a job that’s easy to ignore—until one breaks and the engine stops responding the way it should.
The Mercury Brass Check Valve (Press-In with Sealer Strip)—OEM part number 21-426982—is used in fuel and oil bleed line circuits. These one-way valves support proper directional flow for oiling the main bearings and help bleed off excess fuel/oil mix so the crankcase stays cleaner and the engine comes up on plane harder and more consistently (stronger “out of the hole” performance).
In parts diagrams, you’ll typically see several of these installed around the block as part of the bleed system routing. Replaces all superseded Mercury part numbers: 21-426982, 426982, 42698, or 426981.
What this check valve does in Mercury fuel/oil bleed lines
This check valve is a one-way flow control component in the bleed system. In real-world terms, it helps ensure the fuel/oil mixture in the bleed circuit moves in the intended direction instead of washing back where it shouldn’t.
When the bleed system is working correctly, engines tend to idle cleaner, load up less, and transition more crisply when you punch it—especially on high-output 2-stroke V6 platforms where holeshot and throttle response matter.
Built as a press-in valve with a sealer strip
This is a press-in style brass check valve designed to seat in a machined bore rather than screw in. That press-fit matters on outboards because vibration and pulse loads are constant, and a stable press-in valve stays positioned correctly.
The sealer strip supports sealing and retention once installed, helping prevent bypass leakage around the outside of the valve body—exactly the kind of small leak that can create big drivability inconsistencies on a bleed system.
Common failure: tip-over and impact damage
One of the most common ways these valves fail isn’t age—it’s impact. If a powerhead falls over during removal, transport, or shop handling, these small brass valves can get hit the wrong way and crack, bend, or loosen in the bore. Sometimes they look fine, but they no longer seal or flow consistently. If a powerhead has taken a hit, inspecting and replacing damaged bleed check valves is cheap insurance.
These brass bleed line check valves (OEM Part # 21-42698 2, 426982. 42698, 426981) are widely associated with legacy 2-stroke Mercury Marine, Mariner, and Mercury Racing Outboards: 225X EFI Pro Max, 245 HP Carb, 260 EFI, 280 ROS, S3000, SST-120, and 300 Drag. Mercury Msrine 135 HP V6 (2.5L), 150 HP V6 (2.5L), 150 HP Pro XS 6 CYL (2.5L), 175 HP V6 (2.5L), 175 HP Pro XS 6 CYL (2.5L), V-150 HP (2.5L), V-175 EFI (2.5L), V-200 EFI (2.5L), XR10, and XR-6 / Magnum III. 200 HP XS 6 CYL (2.5L), 200 HP XS 6 CYL (2.5L) ROS, 200 HP XS SST 6 CYL (2.5L), and 2.5XS (2.5L).
SportJet / Jet Drive catalog listings that share the same style bleed hardware in parts lookups:
240 EFI M2 Jet Drive (Pump), 240 EFI M2 Jet Drive (Powerhead), 240 EFI Jet Drive (Pump), 240 EFI Jet Drive (Powerhead), 200 DFI M2 Jet Drive (Pump), 200 DFI M2 Jet Drive (Powerhead), 200 DFI Jet Drive (Pump), and 200 DFI Jet Drive (Powerhead).
Installation notes (do it once, do it right)
Because it’s a press-in component, install quality matters as much as the part itself. Clean the bore, confirm there are no burrs or damage, and press the valve in square using an appropriate driver so you don’t deform the brass body or compromise the sealer strip.
Contact Mike at 714-697-1716 or mike@buckshotracing77.com for technical support.