missing breaking up no vac

Took my car to the track on Sun Made 5 passes on the 4th pass ran fine pulled all the way down the track but on the return road it wouldnt stay running little or no vacum missing and apperd to be very rich (black Smoke) stalled it restated it same thing got back to the pitts shut down looked for a vac leak started back up and seemd to be fine next pass red light but ran it hard any way had a couple of missis but basicly ok drove home and started it today it had all the symtoms again shut it down fired it back up seems to be fine any ideas