Shooting In jpg only does about 6 seconds then stats shooting regular speed..the goes fast again ?
Are you talking about photo or video mode? It sounds like you are talking about shooting photo bursts in continuous photo mode. The "FPS" for photo bursts and the "FPS Override" in ML are two totally different things. "FPS override" is for video, to change the frame rate of the video recording. It has no effect on normal photo taking. ML can't make continuous photo shooting faster, it depends on physical/hardware things like: SD/CF card speed, sensor readout speed, and the mechanics of the physical shutter/mirror mechanism.
The reason it slows down is that the card can't keep up with the rate at which you are taking photos, eventually the camera runs out of extra RAM buffer to temporarily store capture photos and has to slow down and wait for the card to "catch up."