It's difficult to answer because we don't kwow what you mean by "bad quality" ! Described a bit your spectra can help somebody to answer...

Anyway, my impression is that recovery delay is a bit too short (typically 1s) and there are too much complex points (do you mean 256 complex points or 256 td1 point for 128 complex points ?) for aliphatic carbon evolution : you have to put a td1 with a certain limit because carbon evolution occur in a same time as polarization transfert to N (or CO in CBCACONH) that impose a limit (defined by coupling constant) of 3.6ms. Typically, 80 to 160 td1 points is enough to have a good resolution (with a SW of 80 ppm).ppm). Moreover, take account that decrease of S/N occur by splitting of 13C pic by homonuclear coupling if the evolution time is too long.