Problem solved! it was the anti afterfire solenoid under the carb. I changed that. Had my wife go mow for half an hour and no problems. Now when you push the throttle down you also don't get any backfire. So, if you ever have a backfire from deceleration, change that solenoid. Now we have to change the ignition switch as you have to go past the turn off position to get it to die. Thanks for all the great advice.