I was using my 14.5hp briggs and stratton cutting deep thick grass when it bottomed out on uneven ground and stalled. Now it backfires through the carb when I try to start it. I took off the carb and cleaned it out but it didn't seem like it was in bad shape and it didn't fix the backfiring problem.
Any ideas?

The flywheel key may have sheared. Backfiring is a common symptom of being out of time. The key adjusts the timing and can shear off when one hits something solid as you done.

Just a thought. I have had my troubles as well.