Maintain Your Yamaha Fuel System Every 100 Hours

Yamaha outboards demand reliable fuel delivery—especially after extended use. As part of your 100-hour maintenance, inspecting and servicing your fuel system is essential for preserving performance and longevity. Here's how to service both your on-board fuel-water separating filter and the engine-mounted filter element.

1. Replace the Fuel-Water Separating Filter

Locate the external fuel-water separating filter by tracing the fuel hose backward from the engine. Use a filter wrench to remove the old element. Be cautious—it will be full of gasoline. Dump the contents into a clear container to inspect for water and debris. A small amount is normal, but large amounts of water may indicate a larger issue.

If space allows, pre-fill the new filter with fuel and lightly grease the o-ring. Spin it on and hand-tighten just a half turn. This helps with re-priming the system later and ensures a proper seal.

2. Replace the Engine-Mounted Fuel Filter

Move to the engine and locate the clear fuel bowl—usually found on the front of the block. Depending on your model, use a cup wrench or standard tools to remove the bowl. Disconnect the water-in-fuel sensor (if equipped) and inspect the contents just like before.

Check the o-ring on the bowl’s top for cracks or damage. Replace or grease as needed. Install a fresh filter element, reattach the bowl, and tighten with the cup wrench. Prime the fuel system using the primer bulb. Tip: Position the bulb vertically (arrow pointing up) to improve fuel flow.

3. Add Ring Free for System Cleaning

If Ring Free hasn’t been part of your regular fuel treatment routine, now is the perfect time for a “shock treatment.” Double the standard dose (2 oz per 10 gallons of fuel) and pour it directly into the fuel tank fill. It cleans carbon buildup throughout the fuel system. While doing so, inspect the fuel cap’s o-ring—it should seal tightly to keep out rainwater or washdown moisture.

4. Preparing for Storage

If you plan to store your boat after this maintenance, don’t forget to fog the engine using Yamaha STOR-RITE Fogging Oil. Add Yamalube Fuel Stabilizer & Conditioner Plus to the tank to prevent ethanol separation and keep fuel fresh for up to 12 months.

Why Water Appears in Marine Fuel Systems

Ethanol attracts water more than gasoline. Condensation from humid marine environments, rainwater, or damaged filler cap o-rings can introduce water into your tank. Ethanol-blended fuels (like E10) bond with that moisture—leading to phase separation, corrosion, and engine issues.