Generator Runs Rough
In This Guide
A generator runs rough for a reason, and it is not just unpleasant to listen to, it is a warning that the fuel-air mixture is wrong, and running sensitive electronics off unsteady power is a genuine risk. When a generator surges, hunts up and down in speed, or runs unevenly, it is nearly always a fuel-delivery problem, and nearly always the same underlying cause as most generator faults. Here is what is happening and how to fix it.
What Rough Running and Surging Look Like
Rough running shows up in a few related ways: the engine speed rises and falls rhythmically (surging or hunting), the engine misfires or stumbles, the whole unit vibrates more than usual, or the power output flickers. All point to the engine not getting a steady, correct fuel-air mixture.
The Main Cause: A Partially Blocked Carburetor
By far the most common reason. As with most generator faults, stale fuel leaves varnish that partly blocks the carburetor, and a partial blockage is what produces surging specifically. The engine gets slightly too little fuel, the governor opens to compensate, it briefly gets slightly too much, and it hunts back and forth, never settling.
Cleaning the carburetor to restore a clean, steady fuel flow is the fix in most cases.
Cause 2: Stale or Contaminated Fuel
Even without a fully blocked carburetor, degraded fuel burns poorly and unevenly. If the generator has been sitting with the same petrol for months, old fuel alone can cause rough running.
Drain the old fuel and refill with fresh. It is the cheapest thing to try and sometimes all that is needed.
Cause 3: A Dirty Air Filter
The engine needs the right balance of air and fuel. A clogged air filter restricts airflow, richening the mixture and causing rough running, black smoke, and lost power. Checking and cleaning or replacing the filter is quick and cheap.
Cause 4: A Governor Problem
The governor is the mechanism that holds engine speed steady as load changes. If it is out of adjustment or sticking, the engine can hunt and surge even with a clean carburetor. Governor adjustment is a more advanced job and often best left to a technician.
Cause 5: Spark Plug or Ignition
A worn or fouled spark plug can cause misfiring that feels like rough running. It is cheap to check and replace, so it is worth ruling out alongside the air filter.
Fixing It, in Order
1. Fresh fuel
Drain old petrol, refill with fresh. Cheapest first step.
2. Air filter
Clean or replace. Quick and cheap.
3. Spark plug
Check and replace if worn or fouled.
4. Clean the carburetor
If it still surges, this is the most likely fix. Clear the jets and passages.
5. Governor
If all else is clean and it still hunts, the governor may need adjustment, often a technician job.
Rather Have a Real Technician Handle It?
A Wildwood technician comes to your home, diagnoses the generator on site, and gets it running, usually in about an hour. More than 10,000 repairs completed since 2019, with flat rates quoted before we arrive so there are no surprises. When you need power back, you need it back now.