Tiefighter, those are some steep hills, my friend. I barely ever use 1st.  
Disregard, You basically have a similar setup I have, but it still seems to be running a bit lean. Try a moderate white washer mod and see where that gets us. Trim around 1/3 of it, no more for now.

While not saying a hack job on the carb won't help,  popping, or even backfiring on deceleration is a normal characteristic of the single cyl Savage/s40. Most do it right out the showroom door. Suzuki can't do anything to stop it, mainly because they can't hack the carb that is set for emmission standards. How much time and effort a person wants to put in to trying to stop it, is a choice. For myself, I've learned to control it,.....its not a problem.

OTOH, if there is an exhaust leak etc etc that could be making it into a real problem, that is another story I suppose.