If I remember correctly in the archives there was a discussion that the newer Ruby had a smaller "cheater hole" under the smokebox. This seemed to be the difference between the early versions that did not require the door to be open.
This along with the burner modifications will help to correct the problems: http://www.santacruzlumberco.com/MLS_PDFs/SolvingRubyBurnerProblems.pdf
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