The core of what I wanted to point out is the behavior of warp pipes in SMB1, which was outlined quite well here: https://news.ycombinator.com/item?id=21976073

Specifically the part where there's a section in memory somewhere that contains the details of where to warp to, and that varies on Mario's x coordinate.

If a warp pipe in this emulator drops you into an empty level, that sounds to me like that bit of memory isn't getting filled, or there's a jump or load instruction that's supposed to do arithmetic/read args from a register/etc.. and it's not implemented correctly.