In the Indian two-wheeler market, legislation and customers demand for a reduction of emissions and an increase of fuel efficiency. For two-wheelers with engine management systems, a cost-efficient approach for this trend exploits that the periodical fluctuation of the engine speed of single cylinder engines contains useful information about its operating conditions. The present article focuses on the quality of the estimation of combustion phasing and air-fuel ratio of a 125cc single cylinder motorcycle engine, obtained from the evaluation of these fluctuations.The robustness of an oxygen sensor-less port fuel injection system can be increased by using the estimated air-fuel ratio to adapt the parameters of the fuel injection algorithm. The investigations have been carried out only on one bike so far, and have indicated the following accuracies: with the implemented resource optimized algorithm the combustion phasing can be estimated up to ±5°ca accurate with a good reproducibility even after long term operation on a chassis dynamometer. The observed influence of engine temperature was insignificant. The air-fuel ratio feature showed an accuracy of about ±3% in a wide operating range for lambda values smaller than 1.05.Furthermore it is shown that reaching Indian emission legislation Bharat Stage 4 with a PFI system relying only on feed forward control of the air-fuel ratio is possible.