Converting a portable generator to run on propane or natural gas — or adding a tri-fuel kit so it runs on gasoline, propane, and natural gas — trades some peak wattage for fuel that never goes stale. Here’s what actually changes and what to expect:
A tri-fuel kit (brands like Champion, DuroMax, and Winco sell factory versions; Hutch Mountain and US Carburetion sell universal kits) adds a secondary carburetor or a mixer plate ahead of your existing carb, plus a fuel selector valve. Gasoline still gives the most output; propane runs 10–15% lower wattage; natural gas runs another notch below propane, usually 15–20% under gasoline output. If your generator is rated 3500W on gas, budget for roughly 3000W on propane and 2800W on natural gas when sizing your load.
- Expect a real 10–20% power loss switching from gasoline to propane or natural gas — plan your load list around the lower number, not the gasoline rating.
- Propane doesn’t degrade in storage, which is the whole reason to convert if you’re using the generator for emergency standby rather than daily use.
- Natural gas requires a fixed gas line connection, which limits it to standby use at a permanent location — not portable to a job site.
- Universal kits (US Carburetion, Hutch Mountain) fit most small-engine generators with a Honda GX-clone or similar carb, but always match the kit to your engine’s actual carb throat size.
- You lose the ability to easily flip back to pure gasoline on some kit designs — check whether the kit you’re buying keeps the factory carburetor intact or replaces it.
How the Conversion Actually Works
Most tri-fuel kits don’t replace your gasoline carburetor — they add a mixer or secondary carb body in the intake path ahead of it, along with a selector valve that lets you choose which fuel is feeding the engine. Gasoline still runs through the stock carb exactly as before. When you switch to propane or natural gas, a separate regulator meters gas into the intake, and a mechanical or electric solenoid shuts off the gasoline circuit so the two don’t fight each other.
The install itself is mostly mechanical: remove the air filter housing, mount the mixer plate between the carb and the intake manifold, run the fuel line from a propane tank (or a fixed gas line for natural gas) to the regulator, and mount the selector valve somewhere accessible on the frame. Budget an hour if you’ve done small-engine work before, two hours if this is your first time inside a carburetor. Use thread sealant rated for gas, not plumber’s tape alone, on every fitting — a gas leak here is a real hazard, not a minor annoyance.
Why the Power Drop Happens
Gasoline packs more energy per unit of air pulled into the cylinder than either propane or natural gas, so the same engine displacement making 3500W on gas will make less on gas fuels — that’s physics, not a bad kit. Propane typically costs you 10–15% of rated output; natural gas costs another 5% beyond that because it’s delivered at lower pressure than bottled propane. A DuroMax XP12000EH rated 12,000W on gasoline, for example, is commonly derated to around 10,200W on propane in the manufacturer’s own spec sheet — that’s a real number to check against your specific model before you buy a kit, since manufacturers publish these derates for factory dual-fuel units.
The practical fix is simple: size your emergency load list — fridge, well pump, a few circuits, maybe a window AC — against the propane or natural gas number, not the gasoline number stamped on the generator’s data plate. If your load list is already tight against the gasoline rating, a tri-fuel conversion isn’t a good fit; you’ll trip the breaker running on gas.
Propane vs. Natural Gas — Which to Pick
Propane keeps the generator portable — you’re running off standard 20 lb barbecue tanks or a larger 100 lb tank, and it stores indefinitely with zero stabilizer needed. Natural gas ties you to a fixed gas line, meaning the generator effectively becomes a permanent standby unit at one location, but you never run out mid-outage the way you can with a propane tank. If the generator needs to move between a house and a job site or camp, propane is the only practical choice. If it lives permanently next to the house with an existing gas meter, natural gas removes the fuel-supply worry entirely during a long outage.
One more real-world note: natural gas pressure varies by utility and by how many other appliances are drawing on the line at once. If the generator seems to lose power or surge only when the furnace or water heater kicks on, that’s a gas-pressure problem at the meter, not the generator or the kit — worth mentioning to your gas utility rather than chasing it in the carburetor.
Before you buy a kit: Check your generator’s engine specs (bore/stroke or CC rating) against the kit manufacturer’s fitment list. A kit sized for a 420cc engine won’t meter correctly on a 208cc unit, and you’ll fight surging and stalling on gas fuels that has nothing to do with installation quality.