Cummins/Onan 4.0BF Engine

How to read your Cummins/Onan engine serial & model number →

• Wrong Spark
  Fix: Check ignition system
• Wrong Bearin g
  Fix: Replace bearing
• Retie Valve Stuck
  Fix: Lubricate valve
• Poor Qual ty Fuel
  Fix: Use high quality fuel
• Piston Rings
  Cause: Worn or broken
  Fix: Replace piston rings
• Out of Fuel Check
  Fix: Check fuel system
• Oil Too Heavy
  Fix: Change to lighter weight oil
• Oil Le el Low
  Fix: Add more oil
• Low Battery
  Cause: BT I
• Linkage Binding
  Fix: Lubricate or adjust linkage
• Fuel leaks from carburetor.
  Cause: Float level set too high; Dirt under inlet valve; Bowl vent plugged; Collapsed float caused by blowing assembled carburetor with compressed air; Carburetor gummed from storage. Float stuck to screen
  Fix: With fuel bowl removed and carburetor inverted, set float parallel to bowl flange (3/32" clearance); Remove inlet valve, clean seat by rinsing in clean fuel and blow off with compressed air; Remove bowl and blow clean with compressed air; Replace float; Remove fuel bowl and clean with suitable solvent
• Faulty 0 I Pump
  Fix: Replace oil pump
• Engine starts hard.
  Cause: Improper adjustment; No fuel in carburetor; Ch
  Fix: Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Check carburetor drain valve. If no fuel in bowl, clean tank filter and carburetor. Check electric fuel pump operation. Check electric solenoid valve
• Engine smokes and runs rich.
  Cause: Dirty air filter; Improper adjustment; Nozzle boss gasket leaks. Engine runs with power needle seated; Air bleeds in carburetor plugged
  Fix: Clean or replace; Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Remove fuel bowl and replace gasket. Tighten bowl retainer securely; Remove fuel bowl, idle and power needles. Clean thoroughly with compressed air
• Engine runs lean.
  Cause: Improper adjustment; Idle holes plugged; Float level set too low. Low level in fuel bowl
  Fix: Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Remove fuel bowl, idle and power needles. Clean thoroughly with compressed air; With fuel bowl removed and carburetor inverted, set float parallel to bowl flange (3/32" clearance)

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4.0BF.

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.