PC? Chip?

[Me-109]

a proper A/F ratio of 13.8

Actually a richer mixture than this is desirable under acceleration and a leaner mixture under part throttle cruising gives better economy. A leaner mixture leads to higher combustion chamber temperatures though, so it's important not to go too lean. This is where the 'brains' to use throttle sensors in f.i. give economy and power benefits - 3D mapping. The downside of that for tuners is that the engine mapping needs checking at fairly close rpm intervals over more than one load condition and throttle setting - lots of work on a dyno.