issues with switching from rice to buck

I recently began burning UAE buck instead of UAE rice in my DF 520. Since the switch and adjusting feed/air settings, my short feed pipe is always hot and I'm getting some fumes back through the hopper. I know that with my short auger pipe it will be slightly warm, but I can't seem to keep it from overheating and getting slight sulfur smell. Looking through the threads with others burning buck most have to up the air, but not the case for me. Why would that be different in my case? Looking for some ideas or suggestions...

Here's the details:

aquastat settings 200-high 160-low 10-differential
timer 1 minute every 1/2 hour
feed rate 4, air 4.25 (2" ash ring & no unburt coal) ( rice setting were feed rate 5, air 4.5 and feed pipe was cool or slighly warm)
draft over fire .02, flue .04 set with dwyer air meter
8" feed pipe into 55gal hopper with cover
when house calls for heat the recovery time is between 45min to 1.5 hours

heating 1800sq ft 2.5 story single home and DHW, single zone, 11 cast iron radiators, all dual-pane windows, keeping house at 69-70 degrees.

It's because buck doesn't pack as tightly as rice, so there are more air channels for the slight positive pressure of the pot when stoking to push back towards the bin.

mutevelin wrote:8" feed pipe into 55gal hopper with cover

That is making things difficult for you. I hate to sound like Mr. Grouch, but I don't think any combination of settings is going to give you satisfactory performance with that short of an auger and buck. Either extend the auger, or get some rice to mix in with the buck and limp through it.

Sadly, its true. Short augers + buck = Stinky basement. It has been said that you need a minimum of 2' of extra auger past a coupling to keep the gas situation at bay. It has worked for several of my friends.

thanks for the quick replies! i guess i'm sh#t out of luck from the sounds of it and will have to mix in some rice. Still wondering why I'm able to keep my air lower than others burning buck and still have it burn completely...

thanks the input

When I was doing the testing with wood pellets/soft coal and using only a short pipe into a can, it was very easy to see the smoke coming down the pipe. But if I kept 12" of pellets or soft coal above the worm, it was enough to stop the backfeed. Try keeping more coal above the worm at all times.