Why does my generator only run on choke?

Try these first

1. Let it warm up. On a cold day, it's normal to need the choke for the first minute or two.
2. Check the fuel cap vent lever is ON, if your model has one.
3. Check the fuel valve is fully open.
4. Think about the gas. If it's more than a month or two old without stabilizer, swap it for fresh.
5. If it still dies the moment the choke opens, the carburetor needs cleaning.

What the choke actually does

The choke closes off some of the air going into the engine. Less air means a richer mix, with more fuel for each breath. Honda's manual says moving the choke to CLOSED will "enrich the mixture for cold starting."

A healthy engine only needs that extra fuel while it's cold. Honda's steps are to close the choke for a cold start, then "gradually move it to the OPEN position as the engine warms up." For a warm restart, Honda says to leave the choke open.

So if your generator dies or sputters every time you open the choke, the engine isn't getting enough fuel at the normal setting. The choke is covering for it. Something between the tank and the cylinder is starving the engine.

Is some choke normal?

Yes, for a short time. Champion's manual for its 100165 dual fuel model has detents at 100% and 75% choke. It says to move the lever to RUN gradually "over a 2-5 second duration" once the engine starts. It also says not to over-choke, because too much choke leads to spark plug fouling.

What's not normal:

• It needs choke after it has run for several minutes.
• It runs only on half choke, even once warm.
• It surges or hunts when the choke is open, then smooths out when you close it again.

Cause 1: A gummed-up carburetor (the usual one)

Symptom: It starts on choke and runs, but stalls or surges as soon as you open the choke.

Why it happens: The carburetor's fuel passages are tiny. Old gas leaves gum and varnish that partly block them, so less fuel gets through. Champion's storage bulletin says gas left in the carburetor "WILL obstruct and clog the carburetor" if it isn't used or drained within two weeks. Honda's manual says fuel can start to deteriorate "in as little as 30 days."

How to fix it:

Before you start: engine off and cool, spark plug wire off, outdoors, and no flames or sparks nearby.

1. Drain the old gas into an approved can. Many models have a drain screw on the carburetor bowl. Honda and WEN both drain the carburetor through it.
2. Refill with fresh gasoline.
3. Spray carburetor cleaner into the air intake, following the steps in Briggs & Stratton's carburetor guide. Briggs says this solves many problems without taking the carburetor off.
4. Try it again. Run it for a while and see whether it still needs choke.

Our won't start after sitting guide has the full drain-and-clean steps.

If fresh gas and cleaner spray don't fix it, the carburetor needs a full strip-down or replacement. Honda sends carburetor faults to a servicing dealer. Champion calls a full cleaning "technically advanced." If you replace it, buy the exact part for your model number.

Cause 2: Stale or bad gas

Symptom: It sat for a season, and now it runs rough, sputters, or only runs on choke.

Why it happens: Briggs & Stratton calls stale fuel, dirt and debris "the most common cause" of equipment that won't start or run properly. Untreated gas begins to break down after about a month.

How to fix it: Drain it all, including the carburetor bowl. Refill with fresh gas and add stabilizer. Take the old gas to a hazardous waste drop-off.

Cause 3: Fuel can't flow freely

Symptom: It runs on choke for a while, then fades out. Or it runs fine for a few minutes and then starves.

Why it happens: If fuel can't flow freely, the engine runs lean. Check these:

• Fuel cap vent lever. Honda says the vent lever "must be in the ON position for the engine to run." If it's partly closed, the tank can't breathe.
• Fuel valve. Make sure it's fully ON, not halfway.
• Fuel filter. Some models have a strainer in the tank neck or the fuel line. A restricted filter is on Honda's troubleshooting list as a cause of an engine that won't start.

How to fix it: Open the vent and the valve fully. Check the filter, then clean or replace it as your manual describes.

Cause 4: A high-altitude kit at low altitude

Symptom: You took the generator down from the mountains, and now it only runs on choke.

Why it happens: Altitude kits lean out the fuel mix for thin air. WEN's manual says to install one above 3,000 feet. It also warns that running with the kit at lower altitudes "could cause severe engine damage," and says to uninstall it below 3,000 feet.

How to fix it: Check whether a kit is fitted. If you're below the kit's range, have it removed, or swap the standard jet back in, as the maker's kit instructions say.

Don't run it on choke for long

Running on choke is a stopgap, not a fix.

• It fouls the spark plug. Champion links too much choke to spark plug fouling.
• It runs rich and dirty. Briggs & Stratton links black smoke to a flooded carburetor, a dirty air filter or bad fuel. See generator smoking.
• It may not carry a load. An engine that's starved of fuel can bog down or stall when the fridge kicks on.

If you need power during an outage, plug in only the essentials, keep an eye on it, and get the carburetor cleaned as soon as you can.

What not to do

• Don't turn the carburetor's mixture or idle screws unless your manual tells you how. Honda's manual says altering the fuel system or the governor linkage counts as emissions tampering, which is against federal and California law.
• Don't spray starting fluid into the intake to keep it going. No maker manual we checked recommends it.
• Don't bypass the low-oil or CO shut-off if the generator keeps stopping. Those are safety devices, not faults.

When to call a pro

Have it serviced if:

• It still needs choke after fresh gas and a carburetor cleaning.
• You see fuel leaking from the carburetor or air box.
• It's under warranty. Call the maker before you open anything.

Stop it happening again

Most "only runs on choke" problems start in storage. Add stabilizer every time you fill up. Before long storage, drain the carburetor or run it dry. Our how to store a generator guide gives each maker's steps by storage length.

Run it outdoors only, 20+ feet from the house, away from windows and doors: generator carbon monoxide safety.