In-cylinder air motion in an internal combustion (IC) engine has a strong influence on engine combustion, performance and exhaust emissions. In spark ignition engines, large-scale in-cylinder fluid flows like swirl and tumble generated during intake stroke will be later dissipated as turbulence during compression stroke before ignition which promotes flame kernel growth and propagation rate. These types of in-cylinder flows are more desirable in stratified and direct injection spark ignition engines. In IC engines, in-cylinder flows are mainly affected by shape of combustion chamber, intake manifold orientation, compression ratio, crank angle position and engine speed.This paper mainly deals with experimental analysis of in-cylinder tumble flows in a single-cylinder, four-stroke, two-valve engine under motoring conditions using standard and modified intake manifold orientations at an engine speed of 1000 rev/min., during intake and compression strokes using particle image velocimetry. In this study, the axes of the two intake manifolds considered are perpendicular to each other. The two-dimensional in-cylinder tumble flow measurements and analysis are carried out in the combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze tumble flow structures. The tumble ratio and average turbulent kinetic energy are evaluated and used to characterize tumble flows. From the results, it is observed that, at end of compression stroke, modified intake manifold orientation shows about 1.65 and 1.14 times higher tumble ratio and average turbulent kinetic energy respectively compared to standard intake manifold orientation. Present study will be useful in understanding effect of intake manifold orientation on nature of in-cylinder tumble flows under real engine conditions.