Pump will not prime after three minutes:
- Pump housing not filled with water. Fill pump housing with water.
- Static suction head too high. Lower the pump closer to the water.
- Suction hose too long. Reduce suction hose length.
- Leaking suction hose. Repair hose or repair coupler seal.
- Strainer plugged. Clean strainer. To eliminate debris collecting around the strainer, set the strainer in a submerged bucket.
- Internal pump wear or damage. Perform a vacuum test: Fill the pump with water and attach a vacuum gauge to the suction port. Remove the discharge hose and start the pump. Move the throttle to fast. The gauge should read at least 20 inch Hg. If the vacuum is low and the engine speed is correct, there is an internal problem with the pump (worn components, etc.). If the engine speed is too low, there is a problem with the engine (engine worn out, governor problem, etc.).
Low discharge capacity or pressure:
- Maximum engine speed correct:
- Excessive head loss due to restricted discharge hose or very long discharge hose. Increase hose size and/or shorten hose.
- Worn impeller and volute. Pumping water containing abrasives can quickly wear out a Honda general-purpose pump. Pump only clean water or use a Honda Trash pump.
- Damage and poor performance caused by cavitation. See cavitation troubleshooting below.
- Maximum engine speed too slow:
- Engine throttle lever not in fast position.
- Not producing maximum power due to worn engine or governor problem.
Pump Cavitates (grinding noise and impeller worn from pitting):
- The strainer also may be clogged. Keep the strainer clean. To eliminate debris collecting around the strainer, set the strainer in a submerged bucket.
- Static suction head too great and/or suction hose too long or too small in diameter. Always use the shortest suction hose possible. Keep the hose diameter equal to or greater than the pump’s suction port.
Pump housing cracked or broken:
- Vehicle ran over discharge hose. Reposition and/or protect discharge hose.
- Water left in pump housing and allowed to freeze. Always drain water from pump housing after using.
- Water hammer damage caused by shutting water flow off very quickly (or driving over hose) with very long discharge hose length. Shut hose off more slowly or decrease discharge hose length.
Water leaking between pump case and engine:
- Worn mechanical seal. Seal wear is usually caused by pumping water containing abrasives, running the pump dry, or shutting off water flow for a long period of time.
Engine does not turn over:
- Debris lodged in impeller/volute. Always use the Honda-supplied strainer with the pump.
Too small of diameter suction hose causes Cavitations: The sudden formation and collapse of low-pressure vapor (bubbles) across the vanes of the impeller. When the surface pressure on a liquid becomes low enough, the liquid will begin to boil (even at room temperature). With centrifugal pumps, cavitation can occur when the suction vacuum becomes to great enough to allow water vapor or bubbles to begin forming at the impeller. When this water vapor travels through the rapid pressure increase across the impeller, a large amount of energy is released which can cause impeller damage. Minimizing suction head and using the largest practical suction hose diameter will reduce the likelihood of cavitation. You should never use a suction hose with a diameter smaller than the pump’s suction port.
Abrasive fluids can damage the mechanical seal: This is a spring-loaded seal consisting of several parts that seals the rotating impeller in the pump case and prevents water from leaking into and damaging the engine. Mechanical seals are subject to wear when pumping water containing abrasives and will quickly overheat if the pump is run without filling the pump chamber with water before starting the engine. Honda trash pumps contain silicone carbide mechanical seals, designed to withstand abrasive conditions
Sudden shutting off the Discharge can cause water hammering: Water Hammer is energy transmitted back to the pump due to the sudden stoppage of water flowing from the pump. Water hammer is more likely to occur when using a very long discharge hose. If the flow of water at the end of the discharge hose is shut off in less than the "critical time", energy is transmitted back to the pump causing a large pressure spike in the pump housing. Water hammer often results in damage to the pump casing.