Because of the nuclear overhauser effect, primary, secondary, tertiary, and quatenary carbons all have different integral for the same number of carbon atoms.

secondly, due to the low abundance of the C13 isotope, the integral of the same type of carbon has limited accuracy. 

You will probably be better off finding the isomers in the 1H NMR. You only mention the integration, but the coupling could also provide evidence of isomers if the splitting is more complicated than expected (i.e. you get a multiplet instead of triplet, or doublet etc.)  This is a very general statement and must be seen in the context of your compound.

I agree with Yang

Thanks for your response.

But it's worth mentioning that i have 7 secondary carbons and 7 quaternary carbons. Also, I did HMQC and NOESY. would you advise how to get much info from analysis of HNMR, CNMR, HMQC and NOESY.

For HMQC you draw lines to see which H and 13C the signal arises from, see below for an example.

http://www2.chemistry.msu.edu/facilities/nmr/HMQC.html

NOESY same thing just that it is protons on both side, and there can be multiple coupling.

If you have 7 secondary and 7 quartenary carbons, this should be a polycyclic or aromatic compound, there could be other factors affecting the chemical shifts or coupling

The height  of the 13 signal some times are helpful becoz the height may indicate 2 or 3 equivalent carbons, for inatance in para-disubstituted benzene ring. but it is better to confirm from HSQC, HMBC and NOESY. FROM HSQC YOU MAY GET INFORMATIONS REGARDING DIASTEREOTOPIC PROTONS

Many thanks to all