Mercury Carburetor Float Bowl O-Ring 25-16259
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Mercury Carburetor Float Bowl O-Ring 25-16259
Part Number: 25-16259 (short ref: 16259)
Brand: Mercury / Quicksilver
Product Type: Carburetor Float Bowl O-Ring (OEM)
System: Outboard Fuel System / Carburetor
Position: Between carburetor body and float bowl
Quantity Required: 1 per carburetor
GTIN / UPC: 745061117433
Approximate Weight: 5 g
What This Part Does
The 25-16259 is a genuine OEM O-ring that seals the float bowl to the carburetor body on selected small Mercury and Mariner 2-stroke outboard engines. It prevents fuel from leaking at the bowl joint. The O-ring sits in the float-bowl sealing groove and is replaced whenever the bowl is removed for service or the seal shows deterioration.
Compatible Applications
Confirm your engine horsepower, serial number, and carburetor model against the Mercury carburetor diagram before ordering. Mercury used several different carburetor and bowl-seal designs across similar horsepower ranges — do not select this O-ring by diameter or appearance alone.
- Mercury / Mariner 4 HP 2-stroke outboard
- Mercury / Mariner 5 HP 2-stroke outboard
- Mercury / Mariner 6 HP 2-stroke outboard
- Mercury / Mariner 8 HP 2-stroke outboard
- Mercury / Mariner 9.8 HP 2-stroke outboard
- Mercury / Mariner 9.9 HP 2-stroke outboard
- Selected SeaPro and international variants within these horsepower ranges
Serial Number Notice
Mercury used multiple carburetor assemblies across these horsepower ranges. Always confirm by engine serial number and the correct carburetor float-bowl diagram. Nearby fuel-system seals in the same assembly may look similar but carry different Mercury part numbers — match by part number, not appearance.
Diagram Position
Parts diagrams show 25-16259 installed between the carburetor body and float bowl, used alongside:
- Float bowl 803691T01 (later applications)
- Float-bowl screws 162601 (qty 4)
- Drain-screw gasket 16262
When to Replace
- Float bowl is removed for any carburetor service (replace as a matter of course)
- Fuel leakage is visible around the bowl-to-carburetor joint
- O-ring is flattened, permanently compressed, or no longer sealing
- Rubber has hardened, cracked, or become brittle
- Seal is cut, swollen, or distorted on inspection
- Carburetor cleaning reveals deterioration of the existing seal
Installation Notes
- Clean the float-bowl sealing groove and carburetor mating surface thoroughly before installing the new O-ring
- Seat the O-ring evenly in the groove — do not twist, stretch, or pinch it during installation
- Lightly lubricate the O-ring with clean fuel or a compatible O-ring lubricant before assembly
- Confirm the bowl is fully and evenly seated before tightening the bowl screws
- After reassembly, run the engine and inspect for fuel leaks at the bowl joint
Part Number Cross-Reference
- Current OEM: 25-16259
- Short Reference: 16259
Technical FAQ
Q: Can I use a generic O-ring from a hardware store?
A: Not recommended for fuel-system applications. Carburetor O-rings must be compatible with gasoline and ethanol-blended fuels. A generic O-ring may swell, degrade, or fail quickly in contact with marine fuel. Use the OEM part for reliable sealing.
Q: How many O-rings does my carburetor need?
A: 1 per carburetor at the float bowl position. Confirm your carburetor diagram — the same assembly may include additional seals (such as the drain-screw gasket 16262) that should be replaced at the same time.
Q: My engine has the same HP as the list but the O-ring doesn’t look right — why?
A: Mercury used more than one carburetor design within the same horsepower range. If the O-ring size or shape doesn’t match, confirm your engine serial number and the carburetor model number against the parts diagram before ordering.
Parts Desk Insights
Best use case: Order 25-16259 whenever the float bowl is coming off a small Mercury or Mariner 2-stroke carburetor — it’s a low-cost seal that eliminates the risk of reassembling with a compromised O-ring. Most experienced technicians replace it automatically during any carburetor clean or service.
Common issues: The most frequent mistake is ordering by O-ring size rather than part number — Mercury used different bowl seal designs across similar HP engines, so appearance is not a reliable guide. A second common issue is missing the drain-screw gasket (16262) during the same service — both seals are in the same assembly and worth replacing together.
Related Parts
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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