94 gt bkfire issue

[chromeyllastang]

just wanted to get some opinions,my gt started to bkfire lately...its a 306 5spd car was tunned about 6 months ago,i rarely race the car but i did this weeken and in between shifts if bkfires and my friend was behind me and said i shot flames out the xhaust what might be causing this all of sudden..all advice would be appreciated...

 

[Bosko5.0]

timing could be off.
so check timing