FUors are young stellar objects exhibiting record high accretion rates from their circumstellar disc onto the central protostar. Bona fide FUors reach this high accretion state due to an instability-related outburst and stay in the high state for several decades. Due to accretion rates reaching 0.0001 Solar mass per year, their spectral energy distributions are dominated by the active accretion disc at all wavelengths, while the protostar itself has negligible contribution. Thanks to this, small-scale variability observed in their optical light curves can be used to diagnose the accretion disc. Indeed, previous results for the prototype FU Ori indicate that the rotation of inner disc inhomogeneities provides a good explanation for the daily-weekly variability of FUors. Here, we present optical photometric monitoring of three non-embedded FUors, namely FU Ori, V646 Pup, and V2493 Cyg. We analyse TESS photometry obtained in 2018-2022, supplemented by simultaneous ground-based multi-colour observations, following the methodology also used for FU Ori earlier. Our results indicate that, similarly to FU Ori, the majority of the small-amplitude light changes in these objects on time scales of days to weeks are caused by the rotation of inner disc inhomogeneities. We also discuss whether some light curve features could be related to the final stages of mass accretion onto the central star, e.g. in the form of rotating hot spots on the star, or just simple mass accretion rate variations.