So i'm landing on the second block, but after that when i do a full jump while running i jump right into the spiny, and it's not even close. I play on an original NES and use a 3 in 1 cartridge that contains Super Mario Bros., Tetris and Nintendo World cup.

And i am not just bad, because i tested it on emulator and the Nintendo switch thing and it works like a charm. But i really want to do runs on the NES.

I am hoping for someone to clear things up for me. Thanks!

You should jump from the third step. That should land you right under the koopa and jump again. You should pass the stairs successfully.

If I'm not mistaken, that cart was only released in PAL regions, so it's likely that you are running a PAL version of SMB.. The 8-2 issue you are describing happens in that version, because the movement speed of mario is sped up to compensate for the reduced framerate of the console. Any other version, such as the Nintendo Switch release, would be using an NTSC mario rom which makes the 8-2 stairs a lot easier.

You are using a PAL version of the game. The PAL version of the game is much slower and worse in almost every way. You want to either be using a US/J version of the game. If are using an emulator the ROM should be easy enough to find.