A generator that will not start during a power outage is a nightmare scenario — and unfortunately, a common one. The good news is that the vast majority of generator starting failures have simple, fixable causes that a homeowner can diagnose and resolve without a service call. Work through this troubleshooting guide systematically and you will almost certainly identify the problem.

Step 1: Check the Basics

Before assuming a serious problem, confirm the obvious:

  • Is there fuel in the tank? A fuel gauge that reads full after sitting all winter may be inaccurate. Open the cap and visually confirm fuel is present.
  • Is the fuel valve open? Most generators have a fuel shut-off valve. Confirm it is in the OPEN position.
  • Is the choke set correctly? For cold starting, the choke should be fully closed (CHOKE position). After the engine warms up, gradually open the choke.
  • Is the engine switch in the ON position? Simple but easily overlooked.
  • Is the oil level adequate? Most modern generators have a low-oil shutoff that prevents starting when oil is low. Check and add oil if needed.

Step 2: Stale or Contaminated Fuel

This is the most common cause of generator starting failures, particularly after winter storage. Gasoline older than 30–60 days can degrade and leave gummy deposits that clog the carburetor.

How to Fix It

  • Drain the old fuel from the tank completely
  • Add fresh gasoline
  • Try starting again — if the carburetor is not severely clogged, fresh fuel may resolve the issue
  • If it still will not start, the carburetor likely needs cleaning (see Step 4)

Step 3: Check the Spark Plug

A fouled, worn, or incorrectly gapped spark plug is the second most common starting problem. Spark plugs are inexpensive and easy to replace.

How to Inspect

  • Remove the spark plug wire and unscrew the plug with a spark plug socket
  • Inspect the electrode — heavy black deposits indicate a fuel or oil issue; a white or gray electrode is normal
  • Check the gap with a feeler gauge — most generator plugs are gapped at 0.028–0.031 inches
  • Clean carbon deposits with a wire brush or replace the plug if worn

Step 4: Clean the Carburetor

A gummed carburetor from stale fuel is the most common reason a generator cranks but will not start or runs roughly. Cleaning the carburetor resolves most cases without replacement.

Cleaning Process

  • Turn off the fuel valve and drain the carburetor bowl by removing the drain screw
  • Remove the carburetor — typically held by two bolts and a fuel line
  • Disassemble carefully and soak metal parts in carburetor cleaner for 30 minutes
  • Use a thin wire or compressed air to clear jets and passages — do not enlarge openings
  • Reassemble and reinstall

If cleaning does not resolve the issue, replacement carburetors for common generator models are available for $15–$40 and are straightforward to install.

Step 5: Check the Air Filter

A severely clogged air filter restricts airflow enough to prevent starting. Remove the air filter and inspect it — a dark gray or black filter needs cleaning or replacement. Try starting without the filter briefly to confirm whether this is the issue (do not run the generator for extended periods without the air filter installed).

Step 6: Check the Battery (Electric Start)

Electric start generators that click but do not crank, or make no sound when the start button is pressed, typically have a dead battery. Charge the battery with a charger rated for small batteries, or jump-start from a car battery. If the battery will not hold a charge, replace it — most generator batteries cost $20–$50.

Step 7: Compression Check

If all of the above check out and the generator still will not start, low compression may be the issue — indicating internal engine wear or a stuck valve. A compression tester costs $20–$30 at any auto parts store. Most small generator engines should produce 90–120 PSI of compression. Below 90 PSI suggests internal engine problems that typically require professional service.

Preventing Starting Problems

  • Run the generator monthly under load — the most effective prevention
  • Use fresh fuel and add stabilizer for storage over 30 days
  • Change the oil annually
  • Replace the spark plug annually
  • Clean or replace the air filter annually
  • Keep the battery charged with a battery maintainer during storage