Larger than usual mag drop....
Yesterday, started up the aircraft no probs, spent a while getting myself all sorted and letting the engine warm up, then a longish taxi to the hold point (all at low power). When it came to doing the power checks I was getting a large drop off on the left mag only. I tried it several times, each time with exactly the same effect.
I got out of everyone elses way and increased power to the max I could with the brakes holding for 30 secs or so and then did the mag checks again - everything had returned to normal. I then reduced power, mag checks were fine... I tried it at several power settings, carb heat in, out.. every combination I could think of and it was all back to normal.
Was this 'plug fouling' that I seem to recall reading about somewhere, or does it sound like something else?