Generator Won't Start? Where to Look First

Part of our complete Small Engine Troubleshooting Guide.

Work down the list in order and most generators are running again before a carburetor comes off.

1. It Sits Longer Than Anything Else You Own

A mower runs weekly for half the year and a blower comes out a few weekends each autumn. A generator can go two winters without being asked for anything. Whatever fuel went into it the last time the power failed is still sitting in the tank and the carburetor bowl, and that is the single biggest difference between this machine and the rest of the shed.

Ethanol gasoline draws moisture and begins going stale in weeks rather than months. The light part evaporates, what is left turns gummy, and it dries into varnish in passages narrower than a pencil lead. Our guide to ethanol gas and small engines explains why, and it is the reason a unit stored dry starts and one stored full does not.

2. Three Controls Have to Be Right First

More generators come in switched off than broken. These units have more controls than a mower, they get borrowed and moved, and anybody can leave one of them in the wrong position. Before you pull the cord twice, check all four of these:

• The fuel valve. Open it. On many units it sits under the tank or beside the carburetor and gets closed deliberately for storage, which is correct practice and then forgotten.
• The engine switch. Some machines have a separate ignition switch and a fuel valve that look similar, and on others the switch is combined. Set every one of them to run.
• The choke. A cold engine wants full choke and almost no throttle. Once it fires, move the choke off in stages rather than all at once.
• The load. Unplug everything and switch the panel breakers off. A generator asked to start under load often will not, and that is normal rather than a fault.

3. Low Oil Is a No-Start, Not a Warning Light

This is the one that catches people, and it is the reason a generator is not simply a mower with outlets. Most modern units have a low-oil shutdown wired into the ignition circuit, so a low level does not let the engine run badly — it stops the engine starting at all. There is often no light and no sound to explain it.

Check the level on flat ground with the unit level, because a generator read on a sloped driveway or still sitting in a truck bed can show full and trip the sensor anyway. Top up to the mark with the grade the manual asks for, and do not overfill: too much oil causes its own problems. A failed sensor will also hold a healthy engine off, which is a shop job.

4. Stale Fuel and the Carburetor Bowl

If the controls are right and the oil is up, the fuel is next. Drain the tank into a clear jar. Fuel that smells sour, looks like weak tea or has water sitting underneath it is the problem, and nothing else you do matters until it is gone. Fresh fuel costs a few dollars and settles a surprising number of these.

Most generator carburetors are float-bowl units rather than the diaphragm type on a handheld machine, which means there is a bowl with a drain screw on the bottom. Opening it over a jar tells you in thirty seconds whether fuel is reaching the carburetor and what condition it is in. Varnish in the bowl and a blocked main jet are the usual finding, and our guide to small engine carburetor cleaning and repair covers the job.

5. Spark, and the Battery on Electric Start

Pull the plug and look at it. Dry and light brown is healthy. Wet with fuel means it has flooded, usually from too much choke, and it will clear with the choke off and the throttle open. Black and sooty points at a rich mixture or a clogged air filter. A plug that has done several seasons is the cheapest part on the machine and worth replacing on principle.

On an electric-start unit a dead battery is common, because these sit for years on a small trickle charge or none at all. That does not strand you: nearly every electric-start generator keeps a recoil starter as a backup, so try the cord before assuming the engine is the problem. If the cord itself is the thing that gives way, our guide to recoil starters and pull cords covers what breaks and why.

6. It Runs, but the Outlets Are Dead

This is a different fault with a different answer, and it is worth separating because the engine side is fine. Start with the obvious: the main breaker on the panel, any individual outlet breakers, and the GFCI outlets, which trip more easily than people expect. Reset everything and try a known-good lamp rather than the appliance you actually want to run.

If every breaker is set and the outlets still read nothing, the likely cause is that the generator has lost the small amount of residual magnetism it needs to begin making voltage, or that the voltage regulator has failed. Neither is a driveway fix and both are routine bench work. Bring it in rather than guessing at parts.

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What the Symptom Is Telling You

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When to Call the Shop

Opening the fuel valve, topping up the oil on level ground, draining stale gasoline, fitting a new plug and resetting a breaker are all driveway jobs, and between them they account for most of the generators that will not start on the first cold night of an outage. None of them needs a tool you do not already own.

Bring it in when it still will not run on fresh fuel and a new plug, when the carburetor needs cleaning or a kit, when the low-oil sensor is holding off an engine with full oil, when the recoil starter has given up, or when the engine runs and the outlets stay dead. While it is on the bench is also the sensible moment to get the rest of the generator maintenance checklist done, so next winter it starts on the first pull.

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Generator No-Start FAQ

Why won't my generator start after sitting for a year?
Usually the fuel. Ethanol gasoline goes stale in weeks and leaves varnish in the carburetor bowl and the main jet. Check that the fuel valve is open and the oil is up to the mark, then drain the old gas before buying any parts.

Will a generator start if the oil is low?
Most modern generators will not. The low-oil shutdown is wired into the ignition, so a low level, or a level read while the unit is sitting on a slope, stops it firing at all. Check it on flat ground before anything else.

My generator runs but there is no power at the outlets. Why?
Start with the breaker on the panel and any GFCI outlet, which trip more easily than people expect. If both are set and the outlets are still dead, the generator has most likely lost the residual magnetism it needs to make voltage.

Do you repair generators in Richmond, KY?
We do, across Madison County. Carburetor work, fuel valves, low-oil sensors, recoil starters, ignition and charging faults, with pickup and delivery available and a firm quote before any work begins: (859) 661-8877.