the flame might not be due to spark.....
if you aren't sparking, then the fuel is just sitting there on the piston. the more fuel that gets in there, the higher the compression will be and it will eventually explode due to sheer compression. I just gone done helping with a Kawasaki that was getting spark, just not enough. the coils were going bad. Somewhere, you can find what the voltage/ohms/resistance is supposed to be. it can't hurt to check it...
i'm not sure how the timing is setup, however it does sound like it could be a timing issue.