Honda WMP20X Water Pump Maintenance Guide

Honda WMP20The Honda WMP20X is designed for years of trouble-free use, but only if it is maintained properly. This guide can help you perform basic maintenance on this pump without needing to take it in for service.

Working on the WMP20X Safely

Carbon monoxide from the exhaust can kill in high enough concentrations. Always run the pump outdoors and away from doors and windows to prevent carbon monoxide build up. The engine and exhaust can remain hot enough to cause serious burns long after the pump has been shut off. Let the pump cool for several minutes before starting any repairs. Always have the engine turned off when working on the pump, and don’t turn it back on until the repair is completed or the instructions say to do so.

Maintenance Schedule

Before each use, check the oil level in the engine, inspect the air filter for damage and ensure the hoses and strainer are properly installed and free of cracks or tears.

After each use, flush the pump chamber.

The air filter should be cleaned every 50 hours when used in clean environments and more often when operating in dusty areas.

The oil should be changed after the first 20 hours of use, then every 100 hours thereafter. Also, after every 100 hours the spark plug should be inspected and adjusted and both the spark arrester (if installed) and the sediment cup should be cleaned.

Every 300 hours, the paper air filter and the spark plug should be replaced. Valve clearance and idle speed should be checked and the fuel tank and filter should be cleaned and replaced, but Honda recommends taking the pump to a dealer for this work due to their complexity.


The engine in the WMP20X is designed to work with fresh automotive unleaded with an octane rating of at least 86 and containing no more than 10% ethanol or 5% methanol.

Engine Oil

Honda recommends 5W30 or 10W30 oil at temperatures between 20 and 120°F (-10 to 50°C) or SAE 30 at temperatures between 50 and 120°F (10 to 50°C.) This oil should meet API service category SJ or later.

To check the oil level, place the pump on a level surface. Remove the oil filler cap/dip stick, wipe away any oil and reinsert it into the hole without screwing it back in. Withdraw the stick and check the markings. If the level is low, add oil until it meets the edge of the hole.

To change the oil, position a drain pan underneath the motor. Remove the oil filler cap and the drain plug. Once oil has stopped draining from the engine, reinstall the drain plug making sure the gasket is still threaded onto the bolt. Fill the engine with fresh oil and reinstall the filler cap.

Air Cleaner

To inspect the air cleaner, remove the outer wing nut at the top, remove the cover and then remove the inner wing nut. Separate the foam and paper elements and check them for tears or other damage. Wipe away any dirt on the inside cover and wrap the foam filter over the paper filter. Reinstall from the base to the top of the assembly in this order: rubber washer, filter elements, inner wing nut, air cleaner cover and outer wing nut.

To clean the paper filter, tap it gently to loosen any dirt, or blow compressed air through the fins.

To clean the foam filter, wash it in a non-flammable solvent or warm water and a detergent and rinse thoroughly. Once the filter has dried, soak it in clean engine oil and squeeze out any excess.

Spark Plug

To remove the spark plug, disconnect the plug cap and clean out any dirt around the plug. Use a spark plug wrench to unscrew the plug.

If the insulator is damaged or the spark plug is fouled, replace the plug. The plug gap should be between 0.028-0.031 inches (0.7-0.8 mm.)

When reinstalling a new plug, turn it 1/2 turn after the spark plug seats to compress the new sealing washer. If a used spark plug is being reinstalled, it only needs to be tightened 1/8 to 1/4 turn.

Spark Arrester

A spark arrester is optional equipment and may be required to legally operate this pump in some areas due to fire risks. An arrester can be added to any WMP20X when needed.

To access the arrester, unscrew the two 8 mm nuts holding the muffler onto the exhaust port and remove the muffler from the engine. Remove the four 5 mm screws holding on the muffler protector, then lift it off of the assembly. Finally, remove the 4 mm screw holding the arrestor to the muffler and slide it out. Reinstall following these steps in reverse order.

To clean, use a stiff brush to take off any carbon deposits. If there are splits or holes in the arrester, it should be replaced.

Sediment Cup

To clean the sediment cup, begin by turning the fuel valve to the “Off” position. Remove the cup and o-ring, located directly below the valve. Clean these parts in a non-flammable solvent and dry thoroughly. Reinstall the cup and ring, and open the fuel valve to check for leaks.

Where Can I Get Parts for My Honda Water Pump? carries all the OEM parts you need to keep your Honda water pump running from spark arresters to spark plugs.

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