Most dead generators died of stale gasoline, not mechanical wear. Fix the fuel and you have fixed four fifths of the problem.
Store fuel properly →Generator maintenance has an unglamorous truth at its center: the machine that will not start on the night of the storm almost never failed mechanically. It failed because gasoline sat in the carburetor bowl for eleven months, evaporated down to varnish, and blocked a jet the width of a pin. Everything else on the maintenance list matters, but the fuel system is where outages are won and lost.
The Intervals Worth Keeping
Your manual is the authority for your engine, but manufacturers converge on roughly the same schedule for small air-cooled engines. The hours below are engine hours, not calendar time, with one exception that catches people out: oil ages in the sump whether the engine runs or not.
| Task | Interval | Skip it and |
|---|---|---|
| Break-in oil change | First 5 hours | Metal shavings circulate |
| Oil change | 50-100 h or yearly | Bearing wear, seized engine |
| Air filter | Check 100 h | Rich running, fouled plug |
| Spark plug | Yearly | Hard starting under load |
| Exercise under load | Monthly, 15-20 min | Gummed carburetor |
| Valve lash | 250-300 h | Loss of compression |
| Start battery | Check quarterly | Click, no crank |
The one people skip is oil by calendar. A generator that ran 12 hours last year still has oil that has absorbed moisture and combustion acids. Change it annually regardless of the hour meter, and change it while the engine is warm so the contaminants come out with it rather than settling in the bottom of the crankcase.
The Carburetor Habit
Here is the single most valuable thing on this page. When you finish running the generator, close the fuel shutoff valve and let the engine keep running until it dies of starvation. That empties the float bowl. An empty bowl cannot varnish. It takes about a minute and it converts the most common failure mode into a non-event.
If your unit has no shutoff valve — some cheaper models do not — there is usually a drain screw on the bottom of the bowl. Put a container under it, open it, drain, close it. Do that every time and you will never meet an ultrasonic carburetor cleaner. The alternative, disassembling a carburetor to poke a main jet clear with a strand of copper wire, is a rite of passage nobody enjoys twice.
Exercising It Properly
Running the generator for two minutes with nothing plugged in is not exercise; it is theater. An unloaded small engine runs cool, never reaches operating temperature, and can end up with unburned fuel washing the cylinder walls. Give it a real load — a couple of space heaters, a shop vacuum, anything that puts it at roughly half its rated output — and run it 15 to 20 minutes once a month.
- Check oil level before every start. Cold, on level ground, dipstick wiped and reinserted.
- Listen for a change in the note when load comes on. A healthy engine dips and recovers; a sick one hunts.
- Watch for exhaust color. Blue means oil, black means rich, and both mean look closer.
- Confirm the outlets actually deliver voltage with a meter or a plug-in tester, not by faith.
- Finish by closing the fuel valve and running the bowl dry.
Safety: Exercise the generator outdoors, well away from the house, doors and windows. Carbon monoxide from a running engine is odorless and has killed people during a five-minute test run in an open garage. CPSC has linked portable generators to hundreds of non-fire CO deaths since 2009.
Storage Between Seasons
Two schools of thought, and both work if you commit to one. The dry-storage approach: drain the tank and the bowl completely, so there is nothing left to degrade. The wet-storage approach: fill the tank nearly full with stabilized fuel to minimize the air space that causes condensation, run the engine ten minutes so treated fuel reaches the carburetor, then shut the valve and drain the bowl anyway.
Wet storage suits a machine you might need on short notice, because you are not scrambling for fuel at ten at night. Dry storage suits a machine you know you will not touch until spring. What does not work is the hybrid most people default to: half a tank of untreated fuel, valve open, forgotten in a shed.
Also fog the cylinder if the unit is going away for more than a season. A few seconds of fogging oil through the plug hole, then pull the recoil slowly a couple of times to distribute it, and cylinder rust stops being a concern.
Standby Units Are a Different Job
A permanently installed standby generator runs a self-test on a schedule and reports faults to a controller, which removes the exercise chore entirely. What it does not remove is oil changes, coolant checks on liquid-cooled models, battery replacement every three to five years, and the annual inspection that most manufacturers require to keep the warranty valid. Budget a few hundred dollars a year for that service if you are pricing a whole house generator.
The failure mode that dominates standby units is the start battery. It sits on a trickle charge for years, quietly sulfating, and then delivers a single disappointing click. Load-test it, or just replace it on a schedule and stop wondering.
Two Things This Does Not Fix
Maintenance keeps a healthy generator healthy. It does not rescue a unit that was undersized in the first place — a machine run at 100 percent of rated output for days will wear out no matter how clean the oil is. And it does not compensate for a bad install: a generator fed through a daisy chain of undersized cords is being abused every time it runs, and the wear shows up in the alternator windings, not the engine.
Where We Would Put the Effort
If you only adopt one habit, make it the fuel valve. Close it, run the bowl dry, every single time. Second habit: a monthly loaded exercise run with the date written on a card taped to the housing. Third: oil once a year whether it needs it or not. Those three cost maybe two hours annually and they eliminate the overwhelming majority of no-start calls. The rest of the list is real, but it is maintenance in the ordinary sense — this is the part that decides whether you have power at 2 a.m. If the generator has to carry a continuous load like a satellite dish, those hours accumulate faster than you expect and the intervals come around sooner.
Frequently Asked Questions
How often should I start my generator if I never use it?
Once a month, under load, for 15 to 20 minutes. Quarterly is better than nothing but lets fuel sit long enough to matter. A no-load 30-second start is worse than useless because it wets the cylinder without warming the engine.
Why will my generator not start after sitting all year?
Almost always a plugged carburetor jet from evaporated fuel. Check for spark and for fuel reaching the bowl. If you have spark and fresh fuel and it still will not fire, the carburetor needs cleaning — and the bowl needs draining after every run from then on.
What oil goes in a portable generator?
Follow the manual. Most small air-cooled engines call for SAE 30 above roughly 40 degrees and 5W-30 or synthetic 5W-30 in cold weather. Using summer-weight oil in a January outage makes the engine very hard to pull over.
Should I run a generator dry before storing it?
Run the carburetor bowl dry, yes, always. Whether you also drain the tank depends on how quickly you might need the unit. A nearly full tank of stabilized fuel with an empty bowl is the best of both.