A control system for carburation of an internal combustion engine in use conditions comprising following activities: starting the engine with a value of λ equals λ0=λT; constructing a curve ci(α) of the ionization current α as a function of the angular position a of the crank shaft; selecting, on this curve ci(α), a number of points at intervals Δα of the rotation angle a; calculating value z, equal to integral from 0 to 360° of the curve ci(α), is done by summing products Δα×ci for all preselected points; interrupting supply of fuel for some cycles in order to externally modify factor λ0 and take it to value λ1; for value λ1 constructing curve ci(α) and calculating value z1; calculating difference Δz=z1−z0, and if the difference is >Δzref in absolute value, intervening on carburation by increasing the quantity of fuel injected in a case of a positive difference (lean mixture) and by reducing the quantity of fuel injected in a case of a negative difference (rich mixture).