<p>Stringent emission regulations and the demand for improved fuel economy have driven advancements in spark-ignition engines. While direct injection offers better fuel economy and lean-burn combustion, its high cost and packaging complexity limit its adoption in small-bore engines for two- and three-wheelers. Port fuel injection remains preferred for its simpler design and compatibility with modern control strategies. However, during cold start, limited droplet evaporation and persistent wall films hinder combustible mixture formation, leading to misfires and increased unburned hydrocarbon emissions. Additionally, tumble development is restricted by an anticlockwise vortex beneath the intake valve, causing early decay during compression. To examine the influence of in-cylinder flow and injection timing on fuel–air mixture distribution across multiple planes, a computational fluid dynamics framework was developed and validated against experimental data for spray tip penetration (with and without wall impingement) and mixture distribution from planar laser-induced fluorescence. Results show that, in closed-valve injection, vaporized fuel is entrained by intake air and evenly distributed by tumble motion, producing a homogeneous mixture prior to combustion. In contrast, during open-valve injection, the spray enters asymmetrically through the intake valve and interacts with an already developed tumble vortex, confining vapor to one side and sustaining a stratified mixture throughout compression due to weak swirl motion. In addition, a statistical analysis based on the probability density function of the equivalence ratio was evaluated to assess mixture homogeneity across the sectional regions of the in-cylinder domain.</p>