Generator Won't Start | Troubleshooting Guide

Troubleshooting
T
Tom Bradley
Certified Small Engine Mechanic, 25+ Years Experience
Portable generator troubleshooting
Portable generator troubleshooting

Generators often sit unused for months then get pressed into service during emergencies—exactly when you need them most. A generator that won’t start during a power outage creates real problems. This guide covers systematic troubleshooting to get your generator running.

Table of Contents

Pre-Start Checks

Before troubleshooting, verify basic requirements.

Generator ready for troubleshooting Check basics before diving into diagnostics

Essential Checks

  • Fuel: Is there fresh fuel in the tank?
  • Oil: Is oil at proper level?
  • Fuel valve: Is it in the ON position?
  • Choke: Set correctly for conditions?
  • Circuit breakers: All in OFF position for starting?
  • Engine switch: In RUN position?

Starting Procedure

  1. Turn fuel valve ON
  2. Set choke to CLOSED (cold start)
  3. Turn engine switch to ON
  4. Pull recoil or engage electric start
  5. Move choke to OPEN as engine warms

Fuel System Issues

After extended storage, fuel problems are most common.

Old Fuel

Gasoline degrades within 30-90 days. Generators often sit for months, making old fuel the #1 starting issue.

Solution:

  1. Drain old fuel completely
  2. Drain carburetor bowl (usually a screw at bottom)
  3. Add fresh fuel
  4. Try starting

Clogged Carburetor

Varnish from old fuel clogs the tiny passages in the carburetor.

Symptoms:

  • Engine cranks but won’t fire
  • Starts but dies immediately
  • Runs only on choke

Solution: Remove and clean carburetor or have it professionally serviced.

Fuel Valve Issues

The fuel valve (petcock) may be stuck or clogged.

Check: Disconnect fuel line at carburetor. Open fuel valve. Fuel should flow freely.

Solution: Clean or replace fuel valve.

Fuel Filter

Clogged fuel filters prevent adequate fuel delivery.

Solution: Replace inline fuel filter.

Fuel system components Check all fuel system components

Ignition Problems

Without spark, fuel won’t ignite.

Spark Plug Check

  1. Remove spark plug
  2. Connect to plug wire
  3. Ground plug body against engine
  4. Pull starter and observe

Good spark: Strong, consistent blue Bad spark: Weak, yellow, or none

Solution: Replace spark plug if weak or no spark.

Ignition Coil

If new plug still produces no spark, the ignition coil may have failed.

Solution: Test coil with multimeter or replace.

Kill Switch

A faulty kill switch can ground the ignition, preventing spark.

Test: Disconnect kill switch wire. If engine starts, repair or replace switch.

Electric Start Problems

Many generators feature electric start for convenience.

Battery Issues

Generator batteries discharge during storage.

Symptoms:

  • Starter clicks but doesn’t crank
  • Slow cranking
  • No response

Solution:

  1. Check battery voltage (should be 12.6V+)
  2. Charge battery
  3. Clean terminals
  4. Replace if battery won’t hold charge

Starter Motor

If battery is good but starter doesn’t engage:

Check:

  • Starter connections
  • Starter solenoid click
  • Starter motor operation

Recoil Backup

Most electric start generators have manual recoil backup. Use it while diagnosing electric start issues.

Low Oil Shutoff

Many generators have low oil shutoff protection that prevents starting when oil is low.

Oil check on generator Verify oil level before troubleshooting further

How It Works

A sensor detects low oil and grounds the ignition, preventing engine damage.

Troubleshooting

  1. Check oil level on level surface
  2. Add oil if low
  3. If level is correct but still won’t start, sensor may be faulty

Sensor Bypass (Testing Only)

Disconnect the oil sensor wire temporarily. If engine starts, the sensor may be faulty. Don’t operate without oil protection.

Starting Under Load

Generators should start with no load connected.

Procedure:

  1. Turn off all circuit breakers
  2. Disconnect any plugged-in loads
  3. Start generator
  4. Allow to stabilize
  5. Add loads gradually

Overload Protection

Attempting to power too much trips overload protection.

Solution: Reduce connected load before restarting.

Preventive Measures

Regular Testing

Run your generator monthly for 15-30 minutes under light load. This circulates oil, exercises components and ensures readiness.

Fuel Management

  • Use fresh fuel with stabilizer
  • Run generator dry for storage OR
  • Keep stabilized fuel and run monthly

Battery Maintenance

  • Use battery maintainer during storage
  • Check electrolyte levels (flooded batteries)
  • Clean terminals periodically

Frequently Asked Questions

Why won’t my generator start after sitting?

Old fuel is the most common cause. Drain old fuel, clean or drain carburetor bowl and add fresh fuel. If still won’t start, carburetor cleaning is likely needed.

How do I know if my generator spark plug is bad?

Remove plug and test for spark by grounding against engine while pulling starter. No spark or weak yellow spark indicates a bad plug.

Why does my generator start then die?

Usually fuel delivery issues. The carburetor bowl has enough fuel to start, but clogged jets prevent sustained running. Clean the carburetor.

Can I use starting fluid on a generator?

Yes, sparingly for diagnosis. If it fires on starting fluid but won’t run, you have a fuel delivery problem.

How often should I run my generator?

Monthly for 15-30 minutes under light load. This keeps fuel fresh, exercises seals and ensures readiness.

Why won’t my generator start with the electric start but will with pull cord?

Battery or starter issues. Check battery voltage, charge if needed and verify starter connections.

  • Honda Generator Support (honda.com)
  • Generac Power Systems (generac.com)
  • Champion Power Equipment (championpowerequipment.com)

Last updated: January 2026

generator wont start troubleshooting