I can't believe you're selling it! Just spend 30-60 minutes cleaning the carb (very easy to clean) and the mower should run like new. I have a Troy-Bilt mower with that engine and I like it a lot.
I understand, but the carb was cleaned. Truth is, it was never dirty or clogged. It was filled with fresh gas as a new mower, ran once. Sat for 3 weeks and would not start again. Gas drained, replaced with TruFuel, carb cleaned, spark plug replaced. Still wont start. A tiny 'chug' when sprayed with starter fluid. I am done. I understand some folks have time to continue to troubleshoot but it is far more easy to take the $300 loss, be done, move on, lesson learned and buy a quality mower. My last mower lasted 10 years and I gave it away to my church in excellent working order.