I have a DL 50...it was running fine the first 2 gallons when I was using the Fuji oil fuel mixture.  After changing to the Zenoah oil fuel mixture, I been having  a very hard time starting the engine.  The engine would sound like it back fires with a loud sound coming out of the muffer and that is it.  It will not start.  Has anyone had or seen  this  problem before?</p>