  Several radio galaxies are known that show radio morphological signatures
that are best interpreted as restarting of nuclear activity after a period of
quiescence. The conditions surrounding the phenomenon of nuclear recurrence are
not understood. In this paper we have attempted to address this question by
examining the nuclear fuelling characteristics in a sample of restarting radio
galaxies. We have examined the detection rate for molecular gas in a
representative sample of nine restarting radio galaxies, for seven of which we
present new upper limits to the molecular gas mass derived from CO line
observations we made with the IRAM 30-m telescope. We derive a low CO detection
rate for the relatively young restarted radio galaxies suggesting that the
cessation of the nuclear activity and its subsequent restarting may be a result
of instabilities in the fuelling process rather than a case of depletion of
fuel followed by a recent fuel acquisition. It appears that abundant molecular
gas content at the level of few 10^8 to 10^9 solar masses does not necessarily
accompany the nuclear restarting phenomenon. For comparison we also discuss the
molecular gas properties of five normal giant radio galaxies, three of which we
observed using SEST. Despite obvious signs of interactions and nuclear dust
disks none of them has been found to host significant quantities of molecular
gas.
