Propane as a small engine fuel provides a variety of advantages over gasoline. The environmental advantages alone make a propane conversion worthwhile.
Storability — Propane does not go bad and can be stored indefinitely. Modern gasoline, on the other hand, has a shelf life of only a month or two without stability additives, and even then, cannot often be stored longer than six months before degrading.
Cleanliness — Propane is not spilled like gasoline when refueling. It is estimated that Americans spill 17 million gallons of gasoline each year refueling small engines. This represents an environmental hazard as well as a safety hazard, since hot engine parts can cause spilled gasoline to catch fire.
Reduced Emissions — Propane burns much more efficiently (around 90-95% efficient) than gasoline and produces less carbon monoxide and other greenhouse gases. Propane does not evaporate like gasoline, so the evaporative emissions are reduced as well.
Extended Engine Life — Propane has less BTUs of energy per unit than gasoline. While this means that it takes more propane than gasoline to power an engine, the advantages are that less energy is wasted in combustion of propane. Engines run on propane run cooler, which means less stress on internal engine parts and extended engine life.
Extended Service Intervals — Propane does not gum up over time like gasoline, because it is a gaseous and not a liquid fuel, so carburetor problems are not an issue. Propane combustion does not produce excess carbon and gunk like gasoline, and so propane engines typically have a longer interval between oil changes.
Portability — Propane in the disposable cylinders is easier to transport than gasoline.