For the most part, motorcycles and carburetors have come to a parting of the ways. While a few carburetor-equipped bikes are still on the market, the vast majority of street bikes are now equipped with some form of electronic fuel injection, which despite the complication it adds, is both a better way to go, and undeniably here to stay, protests from the Luddites notwithstanding.
Why EFI?
As a rule, internal combustion engines achieve their best performance with air-fuel ratios that hover in the 14.7 to 1 range. Although there's always some latitude, Leaner mixtures tend to degrade performance, while richer ones waste fuel and increase emissions, without substantially increasing performance.
Because lean settings create drivability problems, motorcycles in the pre-emission law days were normally set up on the rich side. This made them easy to start, quick to warm up and provided good performance. True, economy wasn't what it might have been and tail pipe emissions were off the charts, but at the time, gas was cheap and emissions unregulated. As long as the bike ran decently and raw fuel wasn't dripping from the pipes, no one cared how rich their jetting was.
All that changed when the first motorcycle pollution laws were enacted in 1979. Initially, most of the OEM's simply leaned out their jetting, but that led to other problems, and it soon became obvious that a better solution was needed. Initially, it looked like improved carburetors might be the answer and for a time it was. In fact, there are still plenty of carbureted bikes on the market that work just fine.
Unfortunately those days are coming to end, and here's why; Because carburetors rely on fixed orifice jets, overlapping fuel circuits, and volumetric pressure to deliver the correct fuel/air mixture there's not a whole lot of adaptability to them, at least not until you break out the screwdrivers and start changing things, so jetting is often a compromise between slightly lean at some throttle openings and slightly rich at others. This leads to things like slow warm ups, surges at small throttle openings and emission outputs that are borderline legal, and may be pushed over the edge by even the slightest adjustment or change in jetting.
On the other hand, electronic fuel injection systems employ a variety of sensors that tell a computer exactly what the engine is doing at any given moment. After comparing that information to a set of known parameters called a map, the computer determines exactly how much fuel is required to maximize power while creating the lowest emissions, then adjusts the air/fuel ratio accordingly.
Provided the map is accurately written, and with some minor exceptions they're usually pretty good, this allows the engine to receive the ideal mixture under every circumstance, neither so lean that it creates problems nor so rich that it exceeds emission standards, and it's for that reason that they've become the fuel delivery system of choice on everything from scooters to superbikes.
...
>>next page