Longitudenal run out

I have a cheap Chinese lathe (Chester DB8 VS). I’ve turned many round stock which over a short length (say 150mm) has a consistent diameter to about a hundredth of a millimetre. However, whenever I turn a piece say 250mm, the diameter of the first 150mm is pretty good but the last 100mm has a bad taper reducing the diameter at the tailstock end by about 0.16mm. I can’t understand where the misalignment is since the carriage seems to run true in the ways over that distance. The work is held in a carefully cantered four jaw chuck and a live centre in the tailstock by the way. Any help appreciated as I quite like this lathe