I had a bad seize and it locked up the rear tire . I had it softseize twice on another engine but it fired up after it cooled no problem . Soft seize is when your running too lean like too small of a main jet or too much oil . Pull out yoursparkplug and compare it to this chart to get an idea on how the jetting is
http://www.4secondsflat.com/plug_chart.html
Oil pump adjustment to avoid a soft seize
http://49ccscoot.proboards.com/thread/3151