good question, had a hard time getting a clean sample out of my 540c. all narrow spaced concaves, rotor at 600, concaves at an inch,fan at 1250,top sieve at 3/4 inch,bottom at 1/2 inch.air choke wide open. dirty sample in tank with lots of fuzz and head pieces. was an over thrash condition because it was swathed and testing 9.didn't seem like we could get enough air to blow it clean. there is an air door deflector setting on the fan throat but nothing in the book on setting it.70 plus per acre but mog was too high. only time it cleaned up was at 9 in the morning with a bit of dew on the straw.should be a simple job but tried a lot of old tricks and nothing helped.not my first rodeo but finally just quit looking in the tank,pizzed me off because the old cts's were side by side with me and you could have seeded their sample. lets get some answers and make tese things work!