Well carb mixes gasoline with air and lets it in to the combusion chamber. When we move on to efi, first of all car is replaced by injectors. Which fine tune the flow of gasoline. Thus cutting down consumption, preventing overflow and as u people must have noticed that in efi cars u hear a buzzing sound from back of the cars before u apply ignition. That is ecu (electric control unit) letting just the right amount of fuel in to the engine for ignition. Thats why u also get a very quick start up in cars. Moreover over the time when engine detoriates, it also makes up for that to some exten. Reduces pollution as just the right amount of fuel is let in to the engine, so minimum unburnt gases going out of ur tail pipe. There are partial efi cars and full efi cars. In partial efi cars carb is replaced by injectors. But timing is still manual. They come with obd(onboard diagnostics) I ecu. Drawbakcs of this type of efi are, knocking and reduction in pick, unless timing adjusted accurately. Full efi cars are in which even timing is controlled by ecu. They are the one that also benefit from using hi octane, resulting in reduction in fuel consumption and increased pick. pre 1994 efi cars such as honda civic, corrolla, daewoo and many other are partial which in 1995 and beyon we got full efi engine in civics while corrolla has upgraded to full efi in 2003. Efi advantages are reduced maintenance as u do not have to clean carb and also to not tune timing, all the tuning is efi cars are replacing plugs and filters.