What is slowing me?

Hello there, i have used dolphin since early 2013( when my wii died), and i have a question, the OS have influence in the emulator speed?, i was using windows7 x64 last year, but i changed to windows8.1 pro, since then i have noticed that some games that i used to run smoothly dont run as usual, there are something wrong with the OS?, they are some specific settings?, i just wanna play some ssbb

This are my specs:

Cpu: Intel i5 k 655 3.2 GHz
Gpu: Nvidea Geforce GT 640
Ram: Kingston 3,960 mb.
OS: Windows 8.1 Pro

Any help would be appreciated