  We argue that the outbursts of the FU Orionis stars occur on timescales which
are much longer than expected from the standard disc instability model with
\alpha_{c} \gtrsim 10^{-3}. The outburst, recurrence, and rise times are
consistent with the idea that the accretion disc in these objects is truncated
at a radius R_{i} \sim 40 \rsun. In agreement with a number of previous authors
we suggest that the inner regions of the accretion discs in FU Ori objects are
evacuated by the action of a magnetic propeller anchored on the central star.
We develop an analytic solution for the steady state structure of an accretion
disc in the presence of a central magnetic torque, and present numerical
calculations to follow its time evolution. These calculations confirm that a
recurrence time that is consistent with observations can be obtained by
selecting appropriate values for viscosity and magnetic field strength.
