Gas-fueled portable generators are generally the least expensive and the most popular among homeowners. Statistics shows that most consumers buy light-duty low-cost models for home use. A report published several years ago by Frost and Sullivan indicated that more then half of all light duty portable gensets in U.S. are purchased by consumers. At this, more then 98% of purchased portables were gas-powered. Such gensets are currently available in output power range from 500 W to almost 20 kW, with the most popular size being 3 to 10 kW.
Small models are normally powered by 3600 RPM (for the US market) air-cooled, twin cylinder lawn mower type engines. Such RPM is needed to produce 60Hz voltage. Technically speaking, these engines are internal combustion, spark-ignition engines that burn fuel in an enclosed cylinder. The engine's power is produced by the expansion of gases formed by the combustion of a compressed air-fuel mixture. A typical mid-power model has 4 to 8 gallon fuel tank sufficient for 5 to 8 hours run time at rated load.
Built-in fuel tank, air cooling, and the most common type of fuel allows it to run practically anywhere making it truly portable;
It is generally smaller and lighter than other types of gensets.
The high RPM air-cooled engines have relatively short lives, typically about 500 hours of use. If you use such an engine infrequently for emergency purposes, it may remain operational probably for 5 to 7 years, but it is not well suited for continuous operation for days;
Potential carburetor icing when the air is moist;
Required frequent maintenance: draining fuel when not in use, periodic oil changes, replacement of air-cleaner elements,
spark plugs, ignition points, as well as general tune-ups;
Gas pumps may not work during a blackout because they use electric motors to dispense the fuel;
Lower efficiency than diesel gensets
NOTES ON GASOLINE STORAGE
The gas fumes are toxic and highly flammable: storing a large amount gas is unsafe. For example, the NFPA 1:Fire Code (Uniform Fire Code ™) limits the amount of such fuel stored in residential building to 25 gallons. A convenient storage container is DuraMax Flo n'go which includes a 14-gallon rolling can and a transfer pump with 10-foot-long fuel hose for easy refueling. Also note that gasoline has components that oxidize and form gum. As it evaporates, this gum tends to form sticky deposits. Daily temperature changes accelerate this process. Although EPA requires all gasolines to contain a deposit-control additive, it has a typical shelf life of about six months. Chevron says their stabilizers make it possible to store Chevron gas for a year if temperature is controlled. Some third-party stabilizers according to their manufacturers' claims let you keep the fuel fresh for up to 2 years. In any case, be sure to always burn the fuel out of the carberator before storing.
CONCLUSION: WHAT TO CHOOSE
In my view, a generator that works on gasoline is worth considering only if you don't plan to use it frequently, if lowest price is the main object, and you are willing to store a substantial amount of the fuel in case of a wide-spread blackout. Otherwise, you might want to consider more reliable diesel, propane or bi-fuel models.