  We present a single-pulse study of the four-component pulsar J1819+1305,
whose ``null'' pulses bunch at periodic intervals of around 57 times the
rotation period. The emission bursts between the null bunches exhibit
characteristic modulations at two shorter periodicities of approximately 6.2
and 3 times the rotation period, the former found largely in the two outer
components, and the latter only in the first component. Many bursts commence
with bright emission in second component, exhibit positive six-period drift
across the full profile width, and end with 3-period modulation in the leading
component. The 57-period cycle can be modelled geometrically as a sparsely
filled subbeam carousel with nulls appearing whenever our line of sight
intersects a circulating empty region. This interpretation is compatible with
other recent evidence for periodic, carousel-related nulling and appears to
support the physics of a polar-gap emission model for ``drifting'' subpulses,
but the subtle structure of the emission bursts defies an easy explanation.
