FPS drops

[ChaosC57]

I'm playing Mario Kart Double Dash and it's very laggy on the menu and character select screen, but that doesn't bother me. But when I start racing my FPS starts at 40 but then it drops to around 20, goes back up to 40 and then goes back down.

I really want to try and keep a constant FPS going. Any suggestions?

PC SPECS:
AMD Athlon™ 7550 Dual-Core Processor 2.50 GHz
2GB Ram
ATI Radeon HD 5570

Also, half way through the first lap, the music just cuts off and doesn't come back.

[Zee530]

You need a better CPU and the fluctuation could be caused by overheating, check your temps

[idkmybffjill]

A faulty build, perhaps?