Honda GX 390 Engine

Shared across brands: Cummins/Onan, Honda, Pramac, SDMO

How to read your Honda engine serial & model number →

• UNIT RUNS THEN SURGES
  Cause: 1. Loose or worn spark plug lead. 2. Faulty spark plug. 3. Dirty fuel filter or generator set at too steep of an angle. 4. Govenor out of adjustment.
  Fix: 1. Check spark plug lead connection. 2. Remove and clean or replace. 3. Check fuel filter and angle of generator set. 4. Contact a Honda
• UNIT RUNS THEN STOPS
  Cause: 1. Out of fuel. 2. Low oil level. 3. Excess oil.
  Fix: 1. Add fuel. 2. Add oil. 3. Reduce engine oil level.
• Turning the Start/On/Stop or On/Stop switch (depending on model) to the Off position causes the output from the ignition Control Unit to be grounded. This interupts ignition voltage and stops the engine.
  Fix: If switch does not stop engine, check to make sure switch wiring is making proper contact.
• Noisy Generator
  Cause: 1. Worn rotor shaft bearing 2. Rotor and stator rubbing together due to: a. varnish lumps b. rotor misaligned with crankshaft
  Fix: 1. Replace end bearing 2a. Check for varnish lumps between rotor and stator and remove as required. 2b. Follow specified assembly procedures to correct rotor to crankshaft alignment.
• No AC Output Voltage
  Cause: 1. Open AC circuit breaker. 2. Open circuit between stator main coil and AC receptacle. Defective receptacle. 3. Defective Rotor. 4. Defective stator main coil.
  Fix: 1. Locate cause of overload and correct as required. Reset breaker. 2. Check for continuity and correct if circuit is open. Check for defective receptacle/extension cords. 3. Test Rotor coil. 4. Test stator main coil.
• Generator Overheats
  Cause: 1. Generator overloaded due to defective circuit breaker. 2. Airflow restricted due to dirt or debris covering vent openings in cover or adapter. 3. Stator windings covered with oil or dirt. 4. Defective windings in rotor or stator.
  Fix: 1. Replace circuit breaker. Do not exceed specified load when operating set. 2. Clean away all dirt or debris as required. 3. Clean stator windings 4. Test each component for open, grounded, or defective.
• FAILS TO CRANK
  Cause: 1. Low battery. 2. Bad battery connection. 3. Bad start switch. 4. Bad starter motor.
  Fix: 1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections. 3. See Honda Engine Owner’s Manual.
• EXHAUSTING BLACK SMOKE
  Cause: 1. Choke is shut. 2. Dirty air filter. 3. Rich fuel mixture.
  Fix: 1. Open choke. 2. Clean or replace air filter. 3. Reduce engine oil level.
• ENGINE WON’T START
  Cause: 1. Out of fuel. 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plug. 4. Low oil level. 5. No spark.
  Fix: 1. Add fuel. 2. Fully open fuel supply valve. 3. Remove spark plug and clean. 4. Add oil if necessary. 5. See Honda Engine Owner’s Manual.
• CRANKS SLOWLY
  Cause: 1. Low battery. 2. Bad battery connection. 3. Oil is too heavy. 4, Load is connected.
  Fix: 1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections. 3. Replace with recommended oil. 4. Disconnect load while starting.
• AC output voltage too low or too high
  Cause: 1. Engine govenor incorrectly adjusted.
  Fix: 1. Refer to Honda Engine Owner’s Manual.
• AC output voltage only 3 to 18 VAC
  Cause: 1. Defective stator sub coil. 2. Defective rotor winding diode or rotor coil. 3. Open or shorted capacitor.
  Fix: 1. Test stator sub coil for open, shorted, or grounded windings and replace if defective. 2. Replace Diode if defective. Test rotor coil for open, shorted, or grounded winding and defective diode. Replace rotor if defective. 3. Test capacitor for open or short and replace if defective.
• Water leaks from brass valve on pump.
  Cause: Thermal Relief Valve opening to protect pump.
  Fix: Do not run washer with gun trigger closed for more than 3 minutes. Trigger gun to close valve.
• Water inlet screen obstructed.
  Fix: Remove screen, clean or replace.
• Water flows from nozzle when trigger is released.
  Cause: Gun malfunction.
  Fix: DO NOT USE!! See your John Deere dealer.

Compiled from service & troubleshooting documentation across every generator set that uses the Honda GX 390.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.

• Ditch Witch 1330 — Trencher

Other equipment known to use this engine, via filter-application cross-reference — useful for sourcing parts even when your exact machine isn't listed elsewhere on this page.