Yesterday I did weighted pullups with a weight belt for the first time. I was using 15lbs at 5-6 reps each set. Today my lats are super sore. I had been doing lat pulldowns on the machines for a long time. Now I am probably going to stick with the weighted pullups. Before I wouldn't feel it so much in my lats if at all, but mostly in other muscles. I think the weighted pullups put your body in a position to activate the lats more than most exercises.
Just a tip from my experience from doing regular pullups, lat pulldowns on the machine, and now weighted pullups with a weight belt.