Have struggled with the same thing. I always think that closing the bottom sieve too much chokes off the air and the chaffer gets overloaded. Unless you are getting unthreshed Bols then I think it needs lots of air to clean up the sample. If the chaff is kept above the chaffer with air the flax can fall through. I have been as high as 900 on the fan. If you are getting flax in the return I think you need a more open bottom sieve. It can drive a guy nuts. Flax never seems consistent year to year. I know we are always higher than 650 on the fan.

Our wheat tested 20.8 today. Getting real close.....

 

On the afx settings in the manual it says to set the fan at 500. Haha. Can try to increase fan speed as well? I think we have the bottom sieve in slot 3, on the outside of the combine. Yes quite a few unthreshed bola in the sample

 

I believe that we have 3 bars showing in the tailings elevator on the display in the cab

 

Set it just like spring wheat

 

So if I remember the wheat settings. Bottom sieve move to 1/4", fan is 900, and rotor is 1050. Use those settings? Should I leave the concave tight or open it up a bit?

 

One suggestion t try is to rip some flax balls off the stem and throw them on your top sieve and close it until they just drop through or just a bit more . The other thing is to close the front part of the sieve or open it very little as the air seems to escape there and then the chaff falls farther back .Usually run the bottom one at 3/16-1/4