At the start of a BAD part hit "S". This "S"plits the Event at that point. Go further down the Timeline and find where the video comes GOOD, and again hit S. Now highlight/click on this StoS section of the Event and PRESS delete. Gone. If have AutoRipple engaged then the remaining part of the Event will move LEFT to take up the space.
Once you've finished "editing", highlight the whole piece and render to the format you want.