How to Switch a Dual Fuel Generator Between Gasoline and Propane

What a dual fuel generator is

A dual fuel generator can run on either gasoline or propane. The engine is essentially the same, but the fuel system includes a selector switch that directs either gasoline from the tank or propane vapor from a connected tank into the carburetor. The propane connection typically uses a hose that screws onto the generator's inlet, often with a regulator built into the assembly.

The advantage is flexibility: you can start with gasoline and switch to propane when the tank runs low, or you can use propane as your primary fuel because it does not degrade in storage. If you are considering a new unit, our best dual fuel generators guide compares the leading models, and our dual fuel generator advantages article explains the benefits in more detail.

Safety before you switch

Carbon monoxide (CO) is an odorless, colorless gas that can kill without warning. The U.S. Consumer Product Safety Commission (CPSC) warns that one portable generator produces as much CO as hundreds of cars, and it can become lethal in minutes.

Always operate a dual fuel generator outdoors, well away from windows, doors, and vents. The CPSC and the Centers for Disease Control and Prevention (CDC) both recommend keeping at least 20 feet (6 meters) of clearance between the generator and any opening into a building. Never run a generator inside a home, garage, basement, crawlspace, or shed, even if the doors and windows are open.

Install battery-operated CO alarms with battery backup on every level of your home and outside sleeping areas. Test the alarms regularly and replace batteries when you change clocks. For a full rundown of placement and precautions, see our generator carbon monoxide safety and generator safety checklist outdoor use articles.

Switching from gasoline to propane

Shut down the generator and let it cool before touching any fuel components. Disconnect whatever is plugged into the generator's outlets so the engine is not under load when you restart it.

Close the gasoline fuel valve on the generator. If your unit has a fuel shutoff lever, turn it off. Then move the fuel selector to the propane position. On most models this is a lever or knob with clear labels such as 'Gasoline' and 'Propane'.

Connect the propane hose from the tank to the generator's inlet fitting. Make sure the hose is securely threaded and hand-tight. Avoid using tools to over-tighten, as that can damage the O-ring.

Slowly open the propane tank valve. Opening it too quickly may trigger the excess flow valve. Wait a few seconds for the pressure to equalize.

Check the hose and connections for leaks. A soap-and-water solution works: apply it to the joints and look for bubbles. If you see bubbles, close the valve and tighten the connection before proceeding.

Turn the generator's choke to the closed position if the engine is cold, then start the generator using its recoil or electric start. The engine may crank for a few seconds as the propane purges any remaining gasoline from the fuel line. Once it starts, open the choke gradually.

Purging the fuel line

When you switch to propane, the line that previously carried gasoline still contains a small amount of liquid fuel. The engine will run roughly for a short period while it burns through this residue and then settles into smooth operation on propane.

If the engine fails to start after a few pulls, close the choke and try again. This helps clear the line. Once the generator is running, allow it to stabilize for a minute or two before connecting any loads.

Purging is a normal part of switching fuels. It is not a sign of a problem. If your generator uses an electric fuel pump, the purge time is usually shorter because the pump pushes fuel out quickly. In any case, you do not need to manually drain the line before starting.

Switching back to gasoline

To return to gasoline, start by shutting down the generator and letting it cool. Then close the propane tank valve to stop the flow of vapor.

Move the fuel selector switch from propane to gasoline. Open the gasoline fuel valve on the generator. If your unit has a primer bulb, press it a few times to draw gasoline into the carburetor.

Restart the generator using the appropriate starting procedure. As with the switch to propane, the engine may run unevenly for a few seconds while the propane left in the line is consumed. After a moment it should settle into steady operation on gasoline.

If you plan to store the generator, always drain the carburetor or run it until it stalls with the fuel valve closed. See our generator storage preparation guide for details.

Tips and common mistakes

Never attempt to switch fuels while the generator is running. Always shut down, let the engine cool, and then change the fuel source.

Use the correct propane hose and regulator for your generator. Check the manufacturer's manual for the recommended fittings. Do not use a barbecue grill hose unless the generator has a matching connection.

Store propane tanks outdoors and away from the generator when not in use. Keep them upright and protect them from physical damage.

If your generator is equipped with a CO shutoff sensor, do not bypass it. This sensor is designed to protect you from deadly carbon monoxide accumulation. See our article on what is a CO sensor on a generator for details on how it works.

Consider an inverter model if you want quieter operation and cleaner power output. Our best dual fuel inverter generators guide highlights models that handle both fuels efficiently.

What to pick for your use

Questions

Can I switch fuels while the generator is running?

No. Always turn off the generator, let it cool, and then change the fuel selector and connections. Switching while running can cause backfire or damage the fuel system.

Do I need a special regulator to run my generator on propane?

Most dual fuel generators include a propane hose and a regulator in the box. If you are converting a gasoline-only generator, you will need a conversion kit, which is covered in our how-to-convert-generator-to-propane guide.

Why does the engine run rough after switching?

The fuel line still contains traces of the previous fuel. The engine will burn through it in a few seconds and then smooth out. This is normal and not a malfunction.

How far away from the house should I run a dual fuel generator?

Operate it outdoors at least 20 feet from windows, doors, and vents, according to CPSC and CDC recommendations. Always aim the exhaust away from occupied areas and have a working CO alarm nearby.

Is it safe to store propane tanks near the generator?

No. Store propane tanks outdoors, away from the generator and any heat source. Keep them upright and secure them so they cannot tip over.