Why Won’t My Generator Start?

No Fuel

Let’s start with the obvious: did you remember to fill the fuel tank? Did the generator shut off while it was running? Some generators have a built-in gas gauge. It’s connected to a float inside the tank that can get stuck, giving you a false reading. When in doubt, take off the cap and look inside the tank.
 
How do you check how much gas you have in a propane tank? There should be a pressure gauge on the tank, or integrated into the fuel line. Most tank-mounted valves have clear, color-coded markings for fuel pressure. For line gauges, compare the pressure to the minimum requirements for the engine, which should be listed in the owner’s manual.

Oil Level

All engines burn oil, and air-cooled engines burn more oil than water-cooled engines. Generators run for hours unattended, which makes it easy to run low on oil and ruin the engine. To prevent this, modern engines have oil level sensors connected to the ignition system. When the oil gets low, the sensor cuts power to the spark plug, shutting off the engine. Check the oil level and top up as needed.

Choke

The engine needs a rich air/fuel mixture to run when it’s cold, and a leaner mixture when it’s warm. The choke is a butterfly valve with a small hole. Closing the choke restricts the air intake, so there’s less air to mix with the fuel. This gives the engine the rich mix it needs to start. Once the engine is warm, the choke needs to be open to give the engine the fuel/air mix it needs for maximum power. A warm engine will be hard to start with the choke closed.
 
The choke lever is marked with a symbol that resembles a butterfly valve inside the intake. It looks like two vertical lines with a diagonal line in the middle. The placement of this lever differs from model to model. Some engines have a choke lever between the air filter and the carburetor. Others put the lever on the control panel, or integrate it into the power control knob. If it’s connected to the knob, there’s usually a “start” or “choke” position.

Fuel Valve

To keep fuel from leaking during transport, many generators have a fuel shut off valve. This valve is either integrated into the control knob, or attached to the fuel line between the gas tank and the carburetor. This valve should have clearly-marked “on” and “off” positions.

Air Filter

If the air filter is clogged, the engine won’t get the air it needs to run. Open the air filter box and remove the filter. To clean a paper air filter element, tap it against a hard surface. This knocks loose dust off of the filter media. Foam elements can be cleaned with a mild soap and water. Once you wash the filter, let it dry completely. Some foam filters need to be dry, while others need to be soaked in clean engine oil. Check your engine owner’s manual for instructions. Be sure to wipe down the inside of the filter box before you install the air filter elements.

Electrical Loads

Generating electricity during startup puts too much strain on the engine. Be sure to disconnect or turn off electrical loads before starting the generator. Once the engine can run with the choke open, it’s ready to make electricity.

Fuel Cap

If air can’t enter the fuel tank, fuel can’t get out. This air enters through a small hole in the fuel cap. If this hole gets clogged, the pressure inside the tank will drop until gas or diesel can’t be pulled through the fuel line.
 
This problem is easy to miss, since opening the gas cap temporarily fixes the problem. When you remove the cap to check the fuel level, the pressure inside the tank returns to normal. Now, the engine starts and runs for a few minutes, until the pressure in the tank drops again.

Stale and Contaminated Fuel

This is the most common source of starting problems in generators, especially if they’re used for emergency backup. When you go months between starts, it’s easy to let fuel sit inside the generator until it breaks down.
 
Modern gasoline doesn’t age well, no matter what type you buy. Ethanol is hygroscopic. Over time, it absorbs water from the atmosphere. This dilutes the gas, and causes the ethanol to fall out of suspension. This keeps the fuel from igniting, and can lead to corrosion. However, ethanol also inhibits the formation of gums and varnish. Ethanol-free fuels degrade rapidly, leaving deposits that clog carburetor jets and fuel lines.
 
Manufacturers generally recommend using gasoline in carburetor-equipped four stroke engines within one month of purchase, or up to three months if it’s treated with a stabilizer. For two stroke engines, gas should be used within one month, whether or not it’s stabilized.
 
The easiest way to avoid fuel problems is to drain the fuel system when you aren’t sure when you’ll use the generator again. When you’re shopping for a generator, check to see how hard it is to drain the carburetor and the fuel system. Some models have a removable sediment cup on the carburetor. If you open the fuel valve with this cup off of the carburetor, you can drain out every bit of fuel out of the system. Other models have a fuel shutoff switch. This lets the engine use up the fuel left in the carburetor, so it doesn’t have a chance to degrade and clog the jets.
 
Diesel doesn’t degrade with age, but it is a breeding ground for “algae.” These blooms, which are actually fungus and bacteria, clog fuel lines, leaning out the fuel mixture. Fuel treatments are available to kill these blooms. Propane doesn’t degrade with age, making it an excellent fuel source for emergency backup power.
 
With both gas and diesel engines, you can slow down fuel degradation by keeping the tank full. This pushes out air, which contains moisture and oxygen. Both encourage fuel breakdown and biological growth.

Altitude and Fuel Mixtures

For an engine to run properly, it needs the correct ratio of fuel and air. Air gets less dense as altitude increases, so less fuel is needed to get the right ratio. On fuel-injected engine, a MAP or MAF sensor measures incoming air. The ECU uses this measurement to determine how much fuel it should add with the injectors. On carburetor-equipped engines, fuel is controlled by the carburetor jets. If there is too much or too little air entering the engine, the air/fuel mixture can be off enough to keep the engine from running.
 
To correct for this, generator manufacturers offer jet kits for different altitudes. By changing the size of the jets, more or less fuel is added to the air before it enters the engine. Generators usually ship with jets tuned for sea level operation, although you may get high altitude jets if you live in a mountainous area. If you use jets for a lower altitude, the engine will flood when you try to start it. If you use jets for a higher altitude, there won’t be enough fuel to get the engine to fire up.

Spark Plug Problems

If your gas or dual fuel engine doesn’t have spark, it can’t ignite the fuel. Start by checking the spark plug cap. It’s easy to accidentally disconnect the spark plug wire when you’re moving the generator around. Have you repaired your generator recently? Disconnecting the spark plug keeps the engine from firing up if you accidentally bump the starter. You may have just forgotten to hook it back up.
 
Check the condition of the spark plug. A cracked insulator can ground the spark plug to the engine, keeping electricity from reaching the electrodes. Worn and fouled plugs should be replaced.

Vapor Lock

Vapor lock is when the fuel line gets hot enough to vaporize the fuel inside. This creates a gas bubble that prevents liquid fuel from being drawn into the carburetor. This usually happens after shutting off the generator in extreme temperatures. Now that fuel is no longer moving through the line, it has time to absorb heat rising from the engine. Like water, gasoline’s boiling point gets lower at high altitudes. That means you’re most likely to have issues during a hot summer day in the mountains. Ethanol fuel blends also have a lower boiling point, but the difference between E10 and standard gasoline is relatively small.
 
There isn’t much you can do to fix this problem, except let the fuel line cool. Try to move your generator to somewhere with shade. If you have a portable fan, have it blow on the fuel line.

Battery and Starter Issues

All portable generators have a backup recoil starter. However, turning over a big V-Twin is a challenge for the strongest of us. Before you wear yourself out using the pull start, look over the battery and starting system. If you travel with your generator, it’s a good idea to check the connections. Vibrations and bumps can knock them loose, keeping the starter from getting a good connection to the battery.
 
Starters are not built to run continually. Cranking should be limited to a few seconds at a time, with plenty of time in between to let the motor cool. For example, Honda recommends using the starter for a maximum of 5 seconds, followed by 10 seconds of rest. If the starter isn’t kicking over and the battery is charged, make sure the fuse to the starter relay hasn’t blown.
 
Like any battery, lack of use will ruin the one powering your generator’s starter. If you want to preserve your generator’s battery, keep it hooked to a trickle charger when not in use.

I Need a Generator I Can Depend On. Which Brands Are the Easiest to Get Serviced?

While these tips will help you fix common starting issues, you may need a mechanic to solve more complicated starting problems. If you depend on your generator for work or travel, it helps to own something that has good support.
 
No one comes close to Honda’s support. The company has authorized service centers everywhere, and their GX Series engines dominate the commercial equipment market. That means any small engine repair shop should have the skills and parts needed to repair their generator engines, even if they aren’t a dealer. Although Briggs & Stratton’s generators aren’t as popular as Hondas, the ubiquity of their engines gives them a similar advantage.
 
Are Hondas out of your budget? Fortunately, there are several more affordable brands with great support. Wen, Westinghouse and Champion all have extensive dealer networks, making it easy to get service for their products.