i used to have teccy motored push mower - came with the place i bot years ago - PO never maintained it - so a spent a couple hours changing the oil, tune up, ect - now the odd part.
It ran before the tune up, it didnt run after - i tried everything to get it to run - so i put all the old stuff back on ( even the old oil in it) and it fired right up. I never changed the oil or checked it again after that - it was starting to knock a lil bit near the end (i was hoping to see a rod come flying out) - i ended up leaving it with the house when i sold it .