Jet Boat Care - Flushing, Clearing the Pump, Oil, Steering Nozzle and Storage

Yamaha's pre-ride routine, in short:

• Open the engine compartment to air out fuel vapor and run the blower before starting.
• Look for fuel or oil leaks, loose cooling hoses and loose wiring. Make sure battery terminals are clean and tight and the battery is strapped down.
• Check the oil level on both engines. The method depends on the model: Yamaha says screw-in dipsticks are checked with the engine warm, while newer pull-out dipsticks are checked cold. Never fill over the full mark.
• Work the throttle, steering and reverse to be sure they move smoothly without binding.
• Confirm the cleanout plugs are seated and locked, and look at the intake grates and hull.
• Test the stop switch and lanyard on each engine.
• Check the fuel system for leaks by looking and sniffing, and plan your fuel the way Yamaha's checklist does: a third to go out, a third to come back and a third in reserve.

Once you're running, look for a steady stream from each engine's cooling water pilot outlet. A weak or missing stream on one side means that engine's cooling water is restricted, often by debris in the pump or a clogged passage. Shut that engine down and find out why before it overheats.

Weeds, rope, plastic bags and sticks get sucked into jet intakes. Signs: one engine revs higher than the other but pushes less, vibration, or the boat won't plane.

1. Shut off both engines and pull the lanyard.
2. On the trailer or in calm, shallow water, open the cleanout ports (usually under a hatch in the swim platform).
3. Look in with a flashlight and pull out what you can reach. Feel only with the engines off and the lanyard out.
4. Check the intake grate from below and the nozzle from behind.
5. Reinstall and lock the cleanout plugs before you start again. A loose plug lets water into the hull.

If something is jammed between the impeller and the wear ring, or rope is wound tightly on the shaft, the pump may need to come off. That's dealer work on most models. For more detail on inspecting the impeller, wear ring and grate, see our jet pump guide.

Yamaha says to flush the engines with fresh water after every use, in fresh or salt water, because deposits build up in the cooling passages over time and salt left inside keeps corroding. The order matters:

1. With the boat out of the water and level, connect the garden hose adapter to the engine's flush connector.
2. Start the engine first, then turn on the water right away.
3. Run it at a fast idle for about 3 to 5 minutes.
4. Turn the water off first, then blip the throttle a few times to clear water from the exhaust, and stop the engine. Yamaha says not to run more than about 15 seconds after the water is off.
5. Remove the adapter and refit the cap. Repeat on the other engine.

Yamaha warns never to turn the water on before starting or leave it on with the engine stopped: water can flow back through the muffler into the engine. If the engine dies while flushing, shut the water off immediately. If your hose pressure is low, flush one engine at a time rather than splitting the water between both.

Why bother in fresh water? Yamaha explains "dry corrosion": burning ethanol-blended fuel leaves corrosive sulfate salts in the hot exhaust parts. If the water jackets around the exhaust clog with deposits, hot spots form and those salts eat the exhaust from the inside out. Regular flushing keeps the jackets clear. If salt has crusted on the engine itself, Yamaha says a gentle, low-pressure rinse with a plain hose (no spray nozzle) is fine, as long as you keep water away from the air intake and let the engine dry completely before you spray on protectant.

After flushing, Yamaha's post-ride steps are:

• Open the stern drain valves and rinse the bilge, engines and jet units with fresh water, looking for damage as you go.
• Raise the bow on the trailer so the water drains out and the boat can dry.
• Spray the engines with a marine silicone or corrosion-protectant spray to protect rubber parts and fight salt corrosion. Yamaha says this matters even in fresh water.
• Wash the hull with marine boat soap, not dish soap, which strips wax.

On Yamaha boats the sacrificial anodes are usually on or near the jet pump body. Replace them when they're about half gone, use the factory-recommended type, and never paint them. Yamaha also notes that in fresh water anodes can get a thin film of growth that stops them working, so scrub them with a brush and soap when you wash the boat.

With both engines off and the lanyard out, have a helper turn the wheel lock to lock and work the shifter while you watch from behind:

• Both nozzles should move together, smoothly and fully, with no binding or clicking.
• Each reverse bucket should drop fully for reverse and lift fully for forward. A bucket that hangs partway causes drag, poor top speed or weak reverse on that side.
• Look for loose or cracked linkages, frayed cables and worn bushings.

Lubricate grease fittings and pivot points with marine grease if your manual calls for it. If a nozzle or bucket is out of sync with the other side, the cables need adjusting; that's usually a dealer job.

Sand and gravel wear the impeller edges and the wear ring over time. The classic sign is an engine that revs high but the boat feels slow, takes longer to plane or "cavitates." On a twin, compare the engines: if one side always reaches higher rpm with less push, that pump is the suspect. Photograph the impeller edges through the cleanout port: nicks, rolled edges or pitting mean it's time for a dealer inspection. Measuring the wear ring gap and replacing it needs the pump removed and the clearance spec from the service manual.

Yamaha's basics list oil changes every 50 hours, and it says to change the oil and filter before storage rather than waiting for spring, because used oil holds acids and moisture (typical; confirm the interval and oil type for your model in the manual). Yamaha sells oil change kits for its boats. Change both engines at the same time and record the hours in your log. On these engines, use the oil grade your manual specifies; marine four-stroke oils have additives for the corrosion and constant high loads boats see.

• Spark plugs: Yamaha's rule of thumb is to inspect them every 100 hours or every other season. They should be light brown with fairly sharp edges. Replace with the exact type your manual lists.
• Thermostats and pop-off valves: these control engine temperature. Yamaha notes salt deposits or small debris can hold them open, so the engine runs cool and never reaches normal temperature. If one engine runs cooler than the other on the gauge, that's a clue.

Yamaha suggests removing the cleanout access port caps after use to drain water that pools on them, and leaving them out while the boat sits on the trailer at home (it keeps them from sticking in the ports). Reinstall them before you tow any distance, then remove them again when you get home. Always reinstall and lock the cleanout plugs themselves before launching.

For a long layup or winter, Yamaha's list includes:

• Change the oil and filters on both engines.
• Add fuel stabilizer at the storage dose and run it through the system. Yamaha suggests storing with the tank about 7/8 full and never plugging the tank vent.
• Fog the engines with the fogging product your manual recommends.
• Grease all fittings to push out water.
• Charge the batteries fully, check them monthly, and bring them indoors if the boat sits outside in freezing weather.
• On boats with a shower tank, drain it below half; on boats with ballast tanks, loosen the ballast pump caps to drain the pump bodies.
• Clean and dry the boat completely before covering it.

In freezing climates, cooling passages and the exhaust can hold water. Follow your manual's winterizing steps or have your dealer do it, and book early: Yamaha points out that waiting for the first freeze is too late.