strange carbs and cams

This past summer,I ran across some interesting things concerning carbs and cams in Briggs an Stratton engines. First of all a customer brought a riding mower in with a 12 hp Engine the complaint was that it was running wide open whenever it was fired up.I immediately checked all of the linkages going to the carb,governor linkages and so forth.They checked out fine and if I had not seen this before, I would have been stumped. What had happened and apparently was a defect that Briggs was having on some of these engines.The screws that hold the butterfly in the carburetor in place had vibrated out and were sucked into the engine, passed the valves, into the head and either they will imbede themselves into the soft aluminum head or piston, or pass out the exhaust side.AT either rate the engine runs wide open because the butterfly cannot control the gas flow .I had one that had sucked the butterfly into the manifold, intake manifold.I have saw this happen to several 12 and 14 hp engines, so I know it has to be a defect of not putting enough loctite on the butterfly screws Secondly, a customer brought a 15 hp intek, Briggs an stratton in.The symptoms were,it would fire up and run on idle, but would not idle up.I checked the carb, and immediately after finding it to be o.k. Proceeded to adjust the valves,being a overhead valve engine. That done, the symptoms were no better.What was happening was the intake valve was letting fuel in, but the exhaust valve was not staying open long enough to let exhaust out,so Iput exhaust valve way out of tolerances to see what would happen, no change.Immediately the possibility of a bad cam came into mind,but the engine was no more than two years old, then I saw made or assembled in Mexico on the flywheel cap.I pulled the engine, disassembled the bottom crankcase, pulled the cam and wala, one of the lobes was almost completely gone.The exhaust lobe to be exact. I did this to two 15 hp inteks last season,so apparently there is a defect in some of the cams in the newer engines,possibly its been solved by now.Also did this on a 17 hp engine.Note; the replacement cams were of much better quality.