What typically causes carbon soot to build on the air filter, doing my 50 hr service, the manual mentioned to wash the filter if caked in soot, so I did, but what causes this?
Do a search on black mold on the form, I found what was believed to be soot on my deck but with the discussion found on the form I learned that it was mold found in the grass in dry weather. Interesting reading. Hope this helps.
I washed mine this weekend, I had rust fungus real bad last year, and had it all over the tractor several times, but what came out of the filter was black, so my votes exhaust also.