Emission fluxes of CN, C2 and C3 species observed in the coma of some comets are analysed in the framework of Haser model. CN, Cz and C3 production rates are determined using recently derived fluorescence efficiencies and dependence of CN, C2 and C3 production rates on the heliocentric distance is studied. Evidence for a burst type activity around January 15, 1974 in the post-perihelion period of comet Kohoutek (1973f) is observed.