am in Italy at the moment and will be back in India on the 31st July. Then I'll get some pics and post them but here a couple more info on the burners.
They are made from off the shelf water/gas connection tubes and elbows I think, ( as I don't have them here with me) they are 1-1/4" dia. the design is much like the B/W Diagrean just below the colou picture.
the only machined parts are the venturi funnel in ALU which has a dial/disc on a thread. The orifice can be removed and changed over and the burner head has the ring with the small holes on it, and the center is hollow.
As Ben says, I do feel that it is an air intake problem. and I feel it has to do with primary air, as the secondary has a 3-1/2" diameter ( straight hole). (The burner head is 2-1/4" and rests 1-1/2" away from the port)
As far as primary I have tried to open the air to its max, but without success. And at this point I think that ( having tried both smaller and larger orifices) the problem may rest in the size of the burners tubes.
i.e. I think that the smaller orifice "sprays" a cone which is the right size for this tube, but that increasing the orifice size, the "spray" cone gets wider thus reducing the sucking action of the venturi.
As each burner ( and expecially venturi's) are specifically designed for a cerain operation condition ( BTU, pressure, orifice size) I feel that it may well be that the burner size is too small for the orifice I'm trying to use and that with a smaller orifice, which is right for the burner won't give the required BTU's. ( new burners are not a huge issue as being in India I can get them made for a very very reasonable price. )
If I only knew before that the guy who supplied them to me didn't have a clue I would have probably tried to make them on my won or purchased them online...
Till the pictures come bear with me!
P.S here some pics of pots and the open kiln with the 130 deg underfired pots...
hear from you soon guys,