Hi Joeyvek,
It sounds very much like a heat induced issue and as such is more than likely an electrical problem with the HT lead or even the coil. Heat induced issues are always harder to diagnose than problems that are there constantly and can be found quickly.
The rebuilding of these engines is rather simple if you have the relevant tools to do the job, eg. Valve grinding machine, seat cutting tools, boring bar if required, and I hear you saying this is easy ?
Most of these engines only require a light hone of the bore, a new set of rings and a valve grind and then they are away for another lifetime. I really need to do the rings in mine as it's blowing blue smoke in short bursts.
Sadly sometimes it's easier to just do a power plant swap as there are plenty of 2 ~ 2.5 Briggs & Stratton engines out there from other mowers to be had for around $20 ~ $40.
Cheers,
BB
