Predicted term energies for values of the principal quantum number up to 30 and orbital quantum numbers l>=3 in C II, C III and C IV have been obtained using the Ritz and the polarization formulae. Wavelength predictions for lines involving these high-nl term energies together with the corresponding oscillator strengths, calculated by the HFR approach, are also reported in the present paper. Some astrophysical implications of these new atomic data are discussed by means of a comparison with the observed spectra of the planetary nebula NGC 7027.