The MAX IV storage rings are currently under construction in Lund, Sweden and will come into operation in 2016. The rings employ passive harmonic cavities (HCs) to damp instabilities and increase Touschek lifetime by elongating the bunches. The bunch lengthening depends on the filling pattern and the tuning of the resonance frequency of the HCs. The HCs have been designed to operate with a uniform multibunch filling pattern, but a growing interest from the user community to perform timing experiments at the MAX IV storage rings motivate operation with non-uniform filling patterns. We intend to study the performance of the HCs for different filling patterns, e.g. various gap lengths. In addition, we intend to study methods, such as PPRE, with the potential to be operated in the normal multibunch fill pattern.