Looks like I need to try removing and cleaning the orifice! I kind of thought if the flame was this big, that the orifice couldn't be clogged - but sounds like flow and velocity all matter, so hopefully it will help.
I guess I did have it backwards - orange being rich and I was trying to block the shutter. Unfortunately, changing the shutter didn't have any effect either way for me - so no harm.
I definitely cleaned out the burner tube well with a brush - also the combustion tube. So I'm confident that's not the problem in my case. I did not touch the gas valve though - so it sounds like that should be my next step to try tonight.
@Old-Biscuit - If the orifice cleaning doesn't help and I want to test the pressure.... When you say "test port at gas valve" - is that on the water heater gas valve, or on the propane tank valve/regulator? I see about a 1/4" set screw on the water heater valve fairly nearby the output jet - maybe that's a test port?
