Generator Jet Sizes: Adjusting for Altitude and Fuel

What a jet size means on a generator

A carburetor jet is a small, precisely drilled nozzle inside the carburetor that controls how much fuel mixes with air before it enters the engine. On a generator listing, the jet size is almost never stated. Instead, the listing tells you the fuel type, such as gasoline, propane, or natural gas, and the engine's rated output in watts. The jet size is an internal engine detail that the maker's manual covers.

When you see a generator described as dual fuel or tri fuel, the carburetor is set up to handle more than one fuel. The jet size may need to differ for each fuel because gasoline, propane, and natural gas have different energy content and burn characteristics. The maker's manual explains what the unit is designed for and what adjustments, if any, are allowed. For more on fuel types, see our guide to fuel types.

Altitude and jet size

At higher altitudes, the air is thinner, meaning there is less oxygen available for combustion. A carburetor that is tuned for sea level may run rich at altitude, causing rough operation, reduced output, or hard starting. Some generators are sold with a high-altitude jet kit that the owner can install, but the decision to change the jet should come from the maker's manual.

The manual will state the altitude range for which the generator is factory tuned and whether a different jet is recommended for operation above that range. It will also explain the procedure, which typically involves removing the carburetor bowl and swapping the main jet. This is not a routine owner task; the manual may direct you to a qualified service dealer. If you are shopping for a generator for a mountain cabin, consider a portable generator that has altitude guidance in its manual.

Fuel type and jet size

When a generator runs on gasoline, the jet is sized for that fuel's density. Propane and natural gas are gases at atmospheric pressure, so they require a different air-fuel mixture. A dual fuel or tri fuel generator is built with a carburetor that can handle these differences, often through a separate fuel metering system rather than a user-swappable jet.

The listing may say 'dual fuel' or 'tri fuel' to indicate that the generator can run on more than one fuel. The maker's manual will tell you which fuels are approved and whether any jet change is needed when switching. In most cases, the generator is designed to run on all listed fuels without owner adjustment, but the manual is the authority. For a closer look at dual fuel options, browse our dual fuel generator picks.

What the manual covers

The owner's manual for a generator includes a section on the carburetor and fuel system. It will describe the jet size as part of the engine specifications, but it may not list a numeric size. Instead, it will state the recommended jet for the standard altitude and fuel, and it may mention an optional jet for high altitude operation.

The manual also includes a maintenance schedule that lists when to inspect or clean the carburetor. Cleaning a jet is a service task, not a routine owner check. The manual will tell you to contact a qualified service dealer for carburetor work. Always follow the manual's instructions for any fuel system service. If you are comparing generators, read the specs explained article to understand what the listing does and does not tell you.

Why you should not adjust it yourself

Changing a jet size is not a simple adjustment. It requires removing the carburetor, selecting the correct jet, and reassembling the fuel system. A mistake can cause the engine to run too lean or too rich, which may damage the engine or reduce performance. The maker's manual will warn against unauthorized modifications.

If you plan to use a generator at high altitude or with a fuel type not listed on the unit, contact the maker or a qualified service dealer. They can tell you if a jet change is needed and perform the work correctly. This is a service question, not a do-it-yourself project. For general care guidance, see the maintenance checklist.

What to look for on a listing

When shopping for a generator, the listing will tell you the fuel type and the wattage, but not the jet size. If you plan to use the generator at high altitude, look for a listing that mentions 'high altitude' or 'altitude kit' in the features. Some makers include a high-altitude jet in the box, but the listing may not state it.

For dual fuel or tri fuel models, the listing will name the fuels, such as gasoline and propane, or gasoline, propane, and natural gas. The maker's page will have the manual and any notes about jet requirements. Read the manual before you buy if altitude is a concern. You can also compare tri fuel generators to see which models list natural gas as an option.

What to pick for your situation

Questions

Does a generator listing ever state the jet size?

No. Listings state the fuel type and wattage, not internal carburetor details. The jet size appears in the maker's manual or not at all.

Can I change the jet myself to run at high altitude?

The maker's manual will tell you if a jet change is needed and who should do it. In most cases, the manual directs you to a qualified service dealer.

Do dual fuel generators need a different jet for propane?

Dual fuel generators are designed to run on both listed fuels without owner adjustment. The manual explains the fuel system and any service requirements.

What happens if I run a generator at altitude without changing the jet?

The engine may run rich, causing rough operation or reduced output. The manual will state the altitude range for which the generator is tuned.

Is a high-altitude jet kit included with the generator?

Some makers include a kit, but the listing may not mention it. Check the maker's page or manual for what is included in the box.