Why does friend's HDTV make my Xbox 360 lag?

My friend has an 40in LCD HDTV with HDMI, and I have an old 27in CRT type TV with RCA inputs. I play Black Ops a lot on my Xbox 360 with this TV and am a relatively decent player, but when I play on his TV it completely throws me off my game. Everything feels slower, like my character is constantly a half second behind. And when i look left and right there is a much more annoying blur effect. The graphics look great of course, but something is off. I've been reading up on it, but can't find a clear answer. Could it be that his TV has a low response time or refresh rate? (i don't know his exact model, so i don't know its specs). Or is the xbox just not powerful enough to effectively drive the game over HDMI on a large 40in HDTV? Any insight would be much appreciated, Thanks!