Brass should work fine, without tinning. My only thought right now is maybe to have the hole in the juice baffle larger. When I only had a super (rn4081) I used a dummy cart for dripping, and I drilled out the hole in the mouthpiece. It worked a lot better. Maybe go with a 4mm opening and add a 2mm tube to the inside, to act as a baffle. I'll try drawing the mouthpiece with some old school asci art
It's not the best drawing, but you should be able to see what I'm describing.