Predator 670 Fuel Pump: The Essential Guide to Diagnosis, Replacement, and Keeping Your Engine Running

A failing or failed Predator 670 fuel pump is a primary culprit behind frustrating engine problems like hard starting, loss of power, stalling, or complete failure to run. Replacing it with a genuine, high-quality pump correctly is often the definitive solution to restore your engine's performance and reliability.

The reliable Predator 670cc V-Twin engine, commonly found in a vast array of equipment from generators and pressure washers to go-karts and small utility vehicles, depends heavily on a single critical component for operation: its fuel pump. This small, electrically operated mechanical pump plays a vital role. Its sole job is to take fuel from the tank and deliver it under consistent, low pressure to the engine's carburetor at the precise rate needed for combustion. Without adequate fuel flow and pressure, the engine simply cannot run correctly, if at all. Understanding the signs of a failing pump, how to test it, and the proper steps for replacement is essential knowledge for any owner or technician working with the Predator 670 engine.

Recognizing the Symptoms of a Failing Predator 670 Fuel Pump

A fuel pump doesn't usually fail catastrophically without warning. Identifying these signs early can save you from being stranded or damaging your engine:

  1. Difficulty Starting (Hard Starting): The most frequent initial symptom. The engine cranks normally but refuses to start, or it takes prolonged cranking before finally firing up. This happens because the weak pump struggles to supply enough fuel to the carburetor bowls during the starting process.
  2. Engine Stalling or Sputtering: As the pump weakens, it may deliver inconsistent fuel flow, especially under load. You might experience the engine running fine at idle but stumbling, surging, or stalling completely when throttle is applied or a load is placed on the engine.
  3. Loss of Power: Related to sputtering, a failing pump cannot maintain the necessary fuel pressure and volume for the engine to produce its rated power under load. Acceleration feels sluggish, and the engine feels generally weak.
  4. Engine Hesitation: A brief, noticeable pause or "flat spot" when you quickly open the throttle. The pump cannot instantly increase fuel delivery to match the sudden demand for more air.
  5. Engine Surging at Idle: While less common than stalling under load, erratic or weak fuel delivery can cause the engine speed to fluctuate unpredictably at idle.
  6. Engine Dies After Starting: The pump might initially prime enough fuel for start-up but then fail to continue supplying sufficient fuel to keep the engine running, causing it to die shortly after firing up.
  7. Engine Will Not Start At All (Complete Failure): The ultimate symptom. If the pump motor burns out, the diaphragm tears, or valves stick permanently closed, no fuel moves from the tank to the carburetor, rendering the engine impossible to start.

Before Replacing: Crucial Checks to Confirm Fuel Pump Failure

Jumping straight to replacing the pump without diagnosing the issue can lead to unnecessary expense and effort. Rule out other problems first:

  1. Verify Fuel Availability:
    • Is there an adequate amount of fresh fuel in the tank? This seems obvious, but it's frequently overlooked.
    • Is the fuel fresh? Stale fuel, especially gas containing ethanol left sitting for months, can degrade and cause running issues unrelated to the pump. Drain old fuel.
    • Is the fuel cap vent clear? A clogged vent can create a vacuum lock in the tank, preventing fuel flow regardless of the pump's condition.
  2. Inspect Fuel Lines and Filter:
    • Check Fuel Lines: Trace the fuel lines from the tank to the pump and from the pump to the carburetor. Look for cracks, kinks, loose clamps, pinches, or blockages. Replace any damaged or degraded fuel line.
    • Locate and Replace the Fuel Filter: The Predator 670 typically has an in-line fuel filter somewhere between the tank outlet and the carburetor inlet, though sometimes integrated into the tank outlet fitting. A clogged filter severely restricts fuel flow. Always replace the filter when performing any fuel system work, especially if a pump failure is suspected. It's inexpensive preventive maintenance. Use the correct size and flow-rate filter.
  3. Inspect Pulse Line: The Predator 670 fuel pump is a pulse-style pump. It relies on pulses of crankcase vacuum and pressure (delivered via a small rubber hose called the pulse line) to actuate the internal diaphragm. A vital step is checking this specific line:
    • Physical Inspection: Check the pulse line (usually a clear or black hose connecting the crankcase cover to the pump itself) for cracks, brittleness, splits, kinks, or blockages.
    • Security Check: Ensure the pulse line is securely connected at both ends – to the crankcase pulse port and to the nipple on the fuel pump. A loose connection allows air leaks, disabling the pump's operation.
    • Replacement Recommendation: Due to its critical nature and susceptibility to deterioration, replacing the pulse line whenever replacing the pump is highly recommended. Use appropriately sized fuel-rated hose.
  4. Check for Spark: Perform a basic spark test on at least one cylinder. A lack of spark (ignition problem) can mimic fuel delivery failure symptoms. Rule this out quickly.
  5. Check Oil Level: Some Predator engines incorporate a low-oil shutdown sensor. Extremely low oil level can prevent the engine from starting regardless of fuel delivery.

How to Test the Predator 670 Fuel Pump

If you've ruled out fuel supply, lines, filter, pulse line, spark, and oil level issues, it's time to directly test the fuel pump. Always prioritize safety: work in a well-ventilated area away from ignition sources, disconnect the spark plug wire, and relieve any fuel pressure before disconnecting lines.

  1. Visual Inspection: Look at the pump housing for cracks or signs of fuel leakage. Check electrical connections for corrosion or looseness (some pumps have simple connectors, others use bullet terminals or spade terminals within the wiring harness near the pump location).
  2. Bench Test Operation (Recommended):
    • Disconnect the pump's inlet fuel line and outlet fuel line.
    • Disconnect the pulse line from the pump.
    • Connect a short piece of clean fuel line to the pump's inlet fitting. Submerge the other end in a small container of fresh gasoline.
    • Connect a short piece of fuel line to the pump's outlet fitting, directing it into another container or back into the fuel source container (avoid spraying).
    • Obtain a suitable vacuum/pressure test tool (a manual vacuum/pump tester with appropriate adapters).
    • Connect the tester directly to the pump's pulse fitting. You can also carefully use your mouth to create suction and pressure pulses on the pulse hose connection.
    • Apply suction and pressure to the pulse port repeatedly. A functioning pump should visibly and audibly pump fuel from the inlet container to the outlet hose.
    • Listen for smooth operation without excessive internal clicking or grinding noises.
  3. Electrical Resistance Test (If Applicable):
    • If your pump has accessible electrical terminals (many use a two-wire harness connector labeled on the pump itself like "+" and "-" or "M+" and "M-"), you can test the pump motor's coil. Always refer to the specific pump's documentation if possible.
    • Set a multimeter to measure Ohms (resistance).
    • Disconnect the pump harness.
    • Touch the meter probes to the pump's terminals. A typical reading should usually be between 0.5 Ohms and 3.0 Ohms (continuity is present). An extremely high reading (OL or infinite resistance) indicates an open circuit - the motor coil is burnt out. A reading of 0 Ohms indicates a dead short. Both mean the pump is faulty. This test only checks the coil integrity, not the mechanical pumping function.

Choosing the Right Replacement Predator 670 Fuel Pump

If testing confirms pump failure, selecting a quality replacement is critical. Poor-quality aftermarket pumps are a leading cause of repeat failures and ongoing engine issues.

  1. Genuine OEM (Original Equipment Manufacturer) Pumps: Always the preferred choice. Harbor Freight sells Predator parts directly. A genuine Predator pump (Part number 69729 is commonly referenced, but always verify for your specific model!) is engineered specifically for your engine, its fuel pressure requirements, and mounting configuration. Availability is usually excellent.
  2. High-Quality Aftermarket Pumps: If opting for aftermarket, choose reputable brands specializing in small engine parts (like Mikuni, which manufactures OEM pumps for many brands). Research reviews specifically mentioning Predator 670 use. Avoid the cheapest generic options found online – their lifespan and performance are consistently unreliable. Demand requires a pump rated for the 670cc engine size.
  3. Confirm Key Specifications: Ensure the replacement pump:
    • Physically matches your old pump's mounting bolt pattern, inlet/outlet/pulse port sizes, and orientation.
    • Is designed for pulse operation (most Predator 670 pumps are).
    • Has compatible electrical connections (terminal type, harness plug).
    • Is rated for your fuel type (gasoline).

Step-by-Step Guide to Replacing the Predator 670 Fuel Pump

Replacement is generally straightforward. Always refer to your specific equipment manual for engine access steps.

  1. Safety First:
    • Ensure the engine is cool.
    • Disconnect the spark plug wire and secure it away from the plug.
    • Work in a well-ventilated area.
    • Have a fire extinguisher readily accessible.
    • Place absorbent material under the work area.
  2. Relieve Fuel System Pressure:
    • Loosen the fuel cap. If equipped, pinch or clamp the fuel line between the tank and pump, then carefully disconnect that line near the pump, allowing fuel in the line to drain into a container. Have a container ready to catch any residual fuel.
  3. Disconnect Hoses:
    • Disconnect the inlet hose (coming from the tank/fuel filter).
    • Disconnect the outlet hose (going to the carburetor).
    • Disconnect the pulse hose. Note the routing. (Replacing this hose now is strongly advised!)
  4. Disconnect Electrical Connector (if present): Unplug the fuel pump's wiring harness connector.
  5. Remove Mounting Bolts/Screws: Typically two bolts/screws secure the pump to its mounting bracket or engine surface.
  6. Remove the Old Pump: Carefully lift the pump away once all connections are free.
  7. Install the New Fuel Pump:
    • Position the new pump onto its mounting location using any gasket or isolator that came with the pump or was present on the old pump. Do not overtighten. A cracked pump housing will ruin it.
    • Reconnect the inlet hose from the tank/fuel filter to the pump's inlet fitting. Ensure a hose clamp is properly tightened.
    • Reconnect the outlet hose going to the carburetor to the pump's outlet fitting. Ensure a hose clamp is properly tightened. Double-check the direction! Fuel flows from the inlet to the outlet.
    • Install New Pulse Hose: Cut a piece of fuel-rated hose of the correct inner diameter to the exact same length as the old one. Connect one end securely to the engine crankcase pulse port, and the other end securely to the pump's pulse fitting. Ensure no kinks or sharp bends in the hose. Route it away from hot parts and potential snags. (Using new hose prevents air leaks from unseen internal cracks in the old hose).
  8. Reconnect Electrical Connector (if applicable): Plug in the harness securely.
  9. Double-Check Connections: Verify all hose connections are secure and oriented correctly. Ensure no fuel leaks are present.
  10. Reconnect Spark Plug Wire.
  11. Prime and Test:
    • Open the fuel shutoff valve (if equipped).
    • Cycle the ignition switch or start position to energize the fuel pump for several seconds (even without cranking). Listen for a brief hum as the pump runs. You may hear fuel moving through the lines.
    • Attempt to start the engine. It might take a few seconds longer than normal for fuel to reach the carburetor bowls, especially on first startup after replacement. Avoid prolonged cranking without starts; pause and recheck steps if necessary.
  12. Check for Leaks and Operation: Once started, carefully inspect the fuel pump and all connections for any signs of leaks. Observe engine operation – acceleration should be smooth without hesitation or stalling.

Maintaining Your New Predator 670 Fuel Pump

Proper maintenance significantly extends the life of your new fuel pump:

  1. Use Fresh, Clean Fuel: Stale or contaminated fuel accelerates pump wear and internal degradation. Avoid using fuel with high ethanol content ("E15", "E85") whenever possible. Ethanol attracts water, accelerates component breakdown, and can corrode parts. Stick to standard unleaded 87 octane gasoline. Consider fuel stabilizers for any equipment that will sit unused for more than a month.
  2. Replace Fuel Filters Regularly: As part of your routine maintenance schedule (consult equipment manual, often annually or every 100-200 operating hours), replace the in-line fuel filter. A clogged filter forces the pump to work harder, shortening its life. Replace immediately if symptoms of low fuel flow reappear.
  3. Ensure Pulse Line Integrity: Periodically inspect the pulse line during routine maintenance for signs of hardening, cracking, or damage. Replace it proactively if any doubt exists.
  4. Keep the Tank Clean: Avoid letting debris or water accumulate in the fuel tank. Sediment can be drawn into the pump inlet, causing wear and blockages. Strain fuel when filling if stored from a container.
  5. Avoid Running Out of Fuel: Running the engine completely dry forces the pump to run without lubrication and cooling from the fuel flow, increasing wear dramatically. Refill before the tank gets empty.

Troubleshooting After Replacement

In rare cases, issues might persist even after installing a new pump:

  • Engine Still Won't Start: Revisit ALL diagnostic steps above. Confirm fuel delivery: Disconnect the outlet hose at the carburetor momentarily (directing fuel into a container) and briefly crank the engine – fresh fuel should pulse out strongly. Check for spark again. Verify carburetor isn't clogged (dirt or varnish from old fuel in jets/needle seat).
  • Poor Performance/Hesitation: Double-check all hose connections (especially the pulse line) for leaks or incorrect installation. Confirm new fuel filter is installed correctly and the correct type. Confirm genuine or high-quality pump was used. Check carburetor float bowl level adjustment if applicable.
  • Fuel Leaks: Immediately shut off the engine. Check the source. Tighten hose clamps incrementally – be careful not to overtighten and crack fittings. Replace any faulty connections or damaged hoses. Ensure proper sealing washers/gaskets are used.

Conclusion: Reliable Power Depends on Fuel Flow

The Predator 670 fuel pump, while a relatively simple component, is fundamental to the reliable operation of your engine. Recognizing the tell-tale symptoms of failure – hard starting, power loss, stalling – allows for timely intervention. Thorough diagnosis, ruling out fuel supply, filter, and pulse line issues, is essential before replacement. Investing in a genuine OEM pump or a reputable high-quality aftermarket pump is critical for a lasting repair. Following the correct replacement procedure, including using a brand-new pulse line, ensures optimal function. Finally, maintaining a clean fuel system with fresh gas and regular filter changes is the best insurance policy against premature fuel pump problems. By understanding and properly caring for your Predator 670 fuel pump, you ensure your equipment is ready to deliver dependable power when you need it most.

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