Right after the "Carburetor working explained" article, knowing about the air-fuel ratio (or mixture) is as important as it gets. The following article will explain about the importance of Air-Fuel mixture and how to get the perfect balanced ratio. We will only be discussing about the manual tuning on a carburetor, as it's not possible on the electronic fuel injection system (EFI). Air Fuel Ratio (AFR):
In simple terms, the AFR is the ratio between the mass of air and mass of fuel in the air-fuel mixture used in a carburetor at any given moment. The ideal air-fuel ratio is such that in which all the fuel gets burnt completely with absolutely no remaining air, such mixture is also known as Stoichiometric mixture. Basically according to the Stoichiometry, the ratio of air and fuel in the system must be 15:1. This means for 15 grams of air, one gram of fuel is required. So a perfect mixture should combust completely and cleanly with a minimum detonation at a given engine speed and temperature. We can put together as follows for easy understanding,
• =15:1 Ideal mixture
• >15:1 Lean mixture
• <15:1 Rich mixture
But in real time, achieving this perfect ratio using carburetors is not possible. The ratio keeps changing slightly due to the changes in Octane levels in the fuel or/and variation in oxygen content in the air depending upon the atmospheric condition. For example; the air present at the high altitude is obviously deficit of oxygen content and therefore for optimum performance of the engine and the ideal air-fuel mixture the ratio needs to be altered. In these conditions the carburated vehicles get all the bashing since altering the AFR manually all the time is impossible. That's where EFI systems show their upper hand, by using O2 and Lambda sensors. The ratio is changed in real time by using the data from these sensors, this can easily be achieved by a Closed loop Electronic Fuel Injection systems. • >15:1 Lean mixture
• <15:1 Rich mixture
Maintaining The Correct Air Fuel Ratio:
The carbureted motorcycles need frequent minor adjustments, as the atmospheric air won't be the same everywhere. And the fuel from different pumps might also have different octane levels. It is better for the riders to get to know about the working and adjustments of a carburetor, so that the requirement of a mechanic in the middle of a ride can be avoided. Stay tuned as we will be bringing you a detailed and comprehensive article on how to tune carburator for optimum performance.
By: Aravind Rb