I remembered Your having asked this and didn't remember You having gotten a reply, so here goes: The easy way is to run an extra ritch mixture so the furnace is full of carbon monoxide, but I don't have any numbers for You. In the electric furnaces We used for heat treating in the toolroom there was a drip of "carbo fluid" which was alcohol, but I expect any hydrocarbon would work as well. There may be better ways than these however. The premis these methods work on is that there is at least enough hydrocarbon present to combine with all of the oxygen. This is not as fuel efficient as a leaner mixture, and doesn't burn as cleen, but it does solve the problem of an oxidizing atmosphere.

Hey js,
There's a gent who posts on the Brazing & Soldering Thread, Bob Peaslee. He really knows furnace brazing & all the associated heat treat methods and atmosphere parameters and may have some suggestions or opinions for you. I retired from a company who did a tremendous volume of furnace brazing and worked in that dept. for 2 yrs. All his responses from my experience furnace brazing were very accurate and concise. Maybe contact him thru the private message section....Denny