Do you want the grammatical answer or the practical answer?
The grammatical answer is that #1 means that he likes "it" more than he likes me, while #2 means that he likes "it" more than I like it.
The practical answer is that in real life, people say #1 when they mean #2 all the time. This is true to such an extent that I believe that I wanted to convey the grammatical meaning of #1, I'd add the omitted part back in: "All you ever do is talk about that damn motorcylce. Sometimes I swear you like the motorcyle more than you do me!"