VST Float Chamber Gasket – Fits Mercury Mariner Yamaha 150HP-300HP (Replaces 65L-14984-00, 18-0715, 809086)

Product Details

This VST Float Chamber Gasket fits Mercury, Mariner, and Yamaha outboard engines from 150HP to 300HP. Designed for Yamaha 6-cylinder 76-degree V200, V225, S225, and S250 models from 1997–1998, this gasket ensures a proper seal for your VST (Vapor Separator Tank) float chamber.

Direct replacement for OEM part numbers 65L-14984-00, 65L-14984-00-00, 18-0715, 809086, and 25-809086.

• Precision-cut O-ring design for VST float chamber sealing
• Compatible with Mercury, Mariner, and Yamaha fuel systems
• Essential component for preventing fuel leaks and maintaining proper fuel pressure

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Technical Specs

Part Type

VST Float Chamber O-Ring Gasket

Application

Vapor Separator Tank (VST) sealing

Compatible Engines

Mercury, Mariner, Yamaha 150–300 HP outboards

Material

Fuel-resistant elastomer

What's in the Box

• 1 x VST O-Ring

Installation Notes

1. Disconnect the battery and relieve fuel system pressure before beginning work.
2. Remove the VST cover by loosening the mounting bolts in a cross pattern.
3. Carefully remove the old O-ring gasket from the float chamber groove, taking care not to scratch the sealing surfaces.
4. Clean both mating surfaces thoroughly with a lint-free cloth to remove all fuel residue and debris.
5. Lightly lubricate the new O-ring with clean engine oil or gasket sealant if specified by your service manual.
6. Position the new O-ring evenly into the float chamber groove, ensuring it seats properly without twisting.
7. Reinstall the VST cover and torque mounting bolts to manufacturer specifications in a cross pattern.
8. Reconnect the battery, pressurize the fuel system, and inspect for leaks before starting the engine.

Troubleshooting & FAQ

How do I know if my VST gasket needs replacement?

Common signs include fuel odor around the VST, visible fuel weeping from the cover seam, hard starting, rough idle, or loss of fuel pressure. If you're servicing the VST or replacing internal components, always install a new gasket to ensure a proper seal.

Will this fit my Mercury 200HP EFI outboard?

Yes, this gasket fits Mercury and Mariner 150–300 HP models that use the VST fuel system. Cross-reference your current part number (809086 or 25-809086) to confirm compatibility.

Can I reuse the old O-ring if it looks okay?

No. O-rings compress and take a permanent set over time. Reusing an old gasket can result in fuel leaks and inconsistent fuel pressure, leading to performance issues or unsafe conditions.

What's the difference between this and the OEM Yamaha gasket?

This is an aftermarket replacement manufactured to OEM specifications using fuel-resistant materials. It provides equivalent fit and function at a more economical price point.

Do I need to apply sealant to this O-ring?

Typically, no additional sealant is required. A light coating of clean engine oil helps with installation and initial sealing. Always consult your engine's service manual for specific recommendations.

How often should this gasket be replaced?

Replace the VST O-ring any time the VST cover is removed for service, cleaning, or float adjustment. As a preventive measure, consider replacement every 2–3 years or per your manufacturer's maintenance schedule.

Safety & Important Info

• Verify images/specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.