Small Engines (Lawn Mowers, etc.): ride-on-mower, backfire, valve adjustment, tecumseh engine

Question
My engine keeps backfiring, but I have taken the valve out, set the gap and made sure it was seating fine, but still backfires. It is an older engine with the model# TVM170. It is a Tecumseh engine on a MTD frame.

Answer
back  firing as in what  as its shut down????    if this being the case?????    if you throttle it up,  and completely down  to  low idle,  it sometime prevents this.  it boils down to fuel today??   or still a valve  adjustment.   other then  this???   i  have seen this many times  happen  and is basicly   normal.   you may  try a  new spark arester type  muffler.   if  you are running with no  muffler that is  BAD!!!!!  and at times causes this