OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines What B&S is This on my Victa Mustang? Now Faulty.

I've had this Victa Key start with B&S four stroke for over a decade now. I found it in a rubbish skip and it has always been hard to start (hence electric start??) but once going , a real smoothie.
Hasn't got the grunt to tackle tall grass but is (was) perfectly fine for keeping a lawn regularly maintained.
Does anyone know what series this motor is. The mower dates from the late 1980s.
Well after several months, I decided to take it for a run. The oil level never seems to go down and was quite clean when I last checked over a year ago. Anyways, after a lot of cranking over (unusually long time even for this engine) it ran fine for the first couple of minutes but then started to falter and made some metallic sounding knocking noises that sounded suspiciously like a valve timing issue, then eventually stalled. Upon restart it could barely stay on and made the same intermittent metallic internal "hitting" sound before making a mild backfiring sound accompanied by a small shot of flame out the exhaust.
I gave up and pulled out the trusty early 80s 2 stroke Mustang to finish the job with.
I am thinking of just dicing this engine (nice as it is to listen to) and just fitting a powertorque from my Mustang GTS which has a much more worn base than this mower.