We have analyzed spontaneous decay reactions of triply and quadruply charged C-40(z+) and C-41(z+) cluster ions which are formed from C-60 fullerenes by electron-impact ionization. A new but very weak decay reaction for the even-sized carbon cluster ions is observed, namely loss of C-3. The odd-sized cluster ions preferentially decay by loss of carbon atoms and, to a lesser degree, trimers. A weak signal due to Ct loss is observed for C-41(3+). We discuss these decay channels in terms of the geometric structure of these metastable, relatively cold cluster ions.