I searched the net and have not had time to ask the locals yet, so I am asking some of you piston pilots out there what you think.
I took my nephew on his first short x-country for a burger today. He has the bug bad now (all my fault ;-). I have a habit before I park the plane (Cessna 172L) to do a mag check before I put her away. I was the last person to fly this plane and on the run-up this morning my LEFT mag ran rough. I did the normal clearing; 2,000 rpm, watched for the needle drop and put a tiny bit of mixture back in and waited for a slow count to 10. All was cleared and off we went.
We flew to our destination, performed a normal 45° entry to this uncontrolled field and a normal landing; the temp was a lot higher at this airport than it was at home with a density alt of 2,000 inbound and 3,000 leaving. Coming back home, I again performed a run-up and the same thing happened. Only the LEFT mag was rough and the right was fine. I cleared the rough mag again can continued on my way (avoiding parachute jumpers on the way)
I was given a straight-in landing (not my favorite) and I was too high on final. I performed a power-off 40° flap landing. The tower had a citation and a station air inbound for the same and I was placed in front of them. Tower gave me first to land but they told me to keep up my best speed (which I did) until I had to get my airspeed and descent stabilized. Over a small town closer to the runway I pulled the power back with carb heat ON and began my descent with runway in sight.
I had all 40° flaps in on short final and power idle. I will mention that both arriving at the first airport and coming home I always make sure to clear the engine now and again when I am at a low power setting by gently adding power and pulling it back again.
My landing was a very firm short field landing (as it should be with 40° of flaps) I again, did a quick run-up before putting the plane away.
Oh and both mags have been replaced only a few weeks ago. Here is my question...why is it always the LEFT and not the RIGHT mag that runs rough? I have never had the right mag do this to me. I still don't know why they should run rough at all, but at least I am able to clear it each time.