I have an O-360 A-1-A. I have forever had lead fouling problems in bottom spark plugs, as do most if not all O-360's, but argueably worse than most.
At one point, I went to long reach massive plugs in the bottom holes, which helped. Instead of having to clean bottom plugs at 20 hours, I could get away with maybe 30.
Not too long ago, I switched to Iridium fine wire plugs, based on folks stating that these plugs are less prone to lead fouling. Since then (at least somewhere around then-the dang smoke has screwed up my flying so much I'm not sure any more) the bottom plugs seem to foul even worse.
Just recently, the fouling got really bad, and, doing training, I've had to clean the plugs after only 8 hours or so. This is training for float ratings, so a lot of idle power, ups and downs, full power, idle, etc, but nothing different than I've done in past.
Yesterday, the bottom plugs, with about 8 hours on them, were full of clinkers and gunk.
So, any ideas? Is the lower heat range of the fine wire plugs amplifying the problem?
One other note: This engine has always used more fuel than I think it should for a given power setting, but I've been leaning pretty aggressively lately to try to cut down on leading problems. Previous owner said he never leaned, as in never.
Could it be that the carb needs overhaul?