In PFI and GDI engines the tumble motion is the most important charge motion for enhancing the in-cylinder turbulence level at ignition time close to the spark plug position. In the open literature different studies were reported on the tumble motion, experimental and not. In the present paper the research activity on the tumble generation at partial load and very partial load conditions was presented. The added value of the analysis was the study of the effect of the throttle valve rotational direction on the tumble motion and the final level of turbulence at the ignition time close to the spark plug location. The focus was to determine if the throttle rotational direction was crucial for the tumble ratio and the turbulence level.The analyzed engine was a PFI 4-valves motorcycle engine. The engine geometry was formed by the intake duct and the cylinder. The CFD code was FIRE AVL code 2013.1. The intake and the compression phases till TDC were simulated: inlet boundary conditions from 1D simulations were imposed. The modelled fluid was only air because the next step, now in progress, is the analysis of the mixture formation at the same partial load conditions modelling the injection. Once assessed the influence of the throttle valve on both the tumble motion and the turbulence, the authors' focus is the analysis of the mixture formation process and the evaluation of the final mixture index value.