..I purchased a used troybilt fresh start 7 hp mower.The previous owner said he hit a sidewalk with the blade.He said all I would need is a new blade adapter and a spark plug.I bought a new spark plug and it had great spark but the pull rope would almost jerk out of my hand when I tried to start it.I found out the flywheel key had sheared off so I replaced it.The first three times it just barely started,then died right away.I have checked the carb.,and it looked clean and like it was working good,and have tried starting fluid throughout this process.Just fyi,the blade and lower key is off,because I didn't want to spend the money for the blade adapter if the engine wasn't going to run.It then started to backfire out of the air cleaner area,and wouldn't start anymore.I read that it could be the gap on my valves,I have an OHV engine,so I checked and changed the gaps to .004-.006 for the intake and exhaust per briggs and stratton website.It still won't start and I am out of ideas