The answer is,bearing in mind that the bing loves straight air into it
The engine rear is not in the centre of the firewall so using the crankcase join line I moved the whole airbox over so that it was aligned with that ,so the air has a straight run to the carby
I made a new cobra head carby intake with a cross in it to further keep the air straight
As suggested by Don from Jabiru I removed the airfoil type shape from the original plenum chamber that I have and replaced it with a 12mm dowel because the dowel appears to stir the mixture more.maybe a 15mm dowel that was knurled would do an even better job but I am too lazy to try as my egt’s are close enough for me
Further to that I level the carby with The plenum using two rulers to get the rulers parallel with one on the plenum and one on the carby
Jetr is right that the egts change with throttle settings and the speed of the mixture coming in,at full throttle my number 5 mixture is the hottest instead of 2 .at full noise there is a little spread but nowhere near 100 degrees c.will be away for a week or so will get a full throttle reading when I return
Every bit has helped I think but I got the gauge last so don’t really know
I may have uttered a few incantations as well but can’t remember