With the wheel off, do the sprockets turn counter-clockwise easily ?
What kind of bike is it ?
Does it skip after you've been coasting and then start pedaling again ?
Perhaps it is a bit gunked up inside and the pawls are not grabbing all the time. You could try getting some WD-40 inside the freewheel by slowly spinning it backwards and spraying in the groove between the moving cogs and stationary body. Might loosen it up.
Last edited by Homebrew01; 10-26-11 at 12:16 PM.