Optical solitons in multimode fibers exhibit complex dynamics, and peculiar characteristics in terms of pulse duration
and energy, which distinguish them from the single-mode counterpart. We propose a theory for Raman-induced soliton selffrequency shift in multimode fibers, that is compared against experimental data of 1-km multimode soliton propagation. Specific values of pulsewidth and energy are found, at which solitons show long-distance stability and better correspondence with the theory of self-frequency shift; those values depend on the input wavelength, but are not related to the duration of the input pulse. Raman delay is affected by a jitter, characterized by a Gaussian statistical distribution, whose standard deviation tends to stabilize to a constant value for increasing pulse energies.