How to Troubleshoot a Honda WMP20X Water Pump

Honda WMP20X Honda’s WMP20X should be basically trouble free if properly maintained, but what do you do if it stops working? This guide will help you identify and solve common problems for this water pump.

Working on this Pump Safely

Let’s start with the obvious: This is a pump is powerful enough to move large amounts of liquid. If it isn’t working properly, it has the potential to cause serious injury. Pay attention to the warning labels on the pump and never run the pump until the repair is complete or you are specifically instructed to do so.

The engine and muffler can retain heat for several minutes after they have been used and can cause severe burns if touched. Give the motor some time to cool off before starting any troubleshooting.

Finally, remember that like all engines, the exhaust the WMP20X produces contains carbon monoxide. In an enclosed space like a workshop, this gas can build up to a point that it can be lethal.

Engine Won’t Start

Ignition switch is off – The ignition switch is located on the upper right of the starter housing. It needs to be set to “On” to get spark.

Fuel valve off – The fuel valve, located above the starter grip, needs to be set to “On” so that gasoline will reach the carburettor.

Out of fuel – Add fuel to the fuel tank.

Oil level low – The pump will shut off automatically if the oil is low to protect the engine. Check the oil level by removing the oil filler cap located near the bottom of the engine below the muffler. Wipe off any oil, then reinsert the cap without screwing it back in. If the oil level on the cap’s stick is low, add more oil through this opening.

Bad fuel – The engine in this pump needs fresh automotive gasoline with an octane rating of at least 86. If fuel was left in the tank during storage, it will need to be drained. Set the fuel valve to “Off” and place a fuel container beneath the carburettor. Remove the drain screw at the bottom of the carburettor, letting the old gas drain into the container. Reinstall the screw and fill the gas tank with fresh fuel.

Faulty, fouled or improperly gapped spark plug – Remove the spark plug cap and unscrew the plug using a spark plug wrench. The spark plug should be replaced if there is any fouling or the insulator has been damaged. The gap between the electrodes should be between 0.028 and 0.031 inches (0.7 and 0.8 mm.)

Fuel system clog – The pump should be taken to a professional mechanic to find and resolve this problem.

Power Loss

Throttle not set to “Fast” – The throttle lever is located directly below the air filter and above the starter handle.

Air filter clogged – Shut off the engine and remove the air cleaner assembly by taking off the top wing nut followed by the air filter cover and inner wing nut. Separate the foam filter element from the paper filter. Clean the paper element by gently tapping it to loosen dirt or by spraying the filter with pressurized air. Clean the foam element with a non-flammable solvent or a mix of household detergent and water. Once the foam has dried completely, dip it in clean engine oil and squeeze out any excess. Wipe off the inside of the cover before reinstalling.

Bad fuel – See the “Bad Fuel” section above.

Fuel system clog – The pump should be taken to a professional mechanic to find the clog and clear it.

Pump Doesn’t Pump

Strainer clogged – Shut off the engine and pull the suction hose out of the water. Clean off any debris build-up on the strainer.

Suction hose clamp loose – Make sure the hose is pressed flush against the pump inlet and tighten the clamp.

Sealing washer not installed on suction hose – The sealing washer goes between the hose and the pump inlet.

Suction head too high – The “head” is the height difference between the height of the water’s surface and where it is being pumped. Although this pump can handle a head up to 105 feet (32 m) under ideal conditions, it takes less power to move water through the discharge hose than the suction hose. Moving the pump lower and letting the discharge hose make up more of the height difference will improve performance.

Pump needs to be primed – Shut off the engine, then fill the priming tank, located directly above the pump, with water.

If the pump still isn’t moving water, it needs to be serviced by a mechanic.

Where to buy Honda Water Pump parts

Figured out what’s wrong, but don’t have the parts you need to fix it? has what you’re looking for. They carry OEM parts for every model of Honda small engine equipment including pumps like the WMP20X.

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