Wow, that is unusual. I am running 8 and a bit:1, standard 276 carbs with 190 main jets and 34º advance on a modern BT-H on my Rap. My post war Comet is running similar comp. with coil ignition on 36º and 930 concentric with 220 main. What sort of adv/ret mechanism are you using Howard and have you checked the range? One has to be careful comparing jet sizes on different types of carburetters as they are not equivalent (equijet?). The silencer also plays a big part in obtaining the correct jetting on our bikes.
I'm using Pazon. I have to say I'm suspicious of the timing mark, but based on how Pazon recommend setting the timing, it's now on 40 degrees.......... and I intend to try 42 when I can. Every time I advance the timing it seems to improve and 34 (if that's what it was) was very wrong. Peter Appleton is running 40, and that's what prompted me to go that high, but I've had no sign of pinging yet, and the old addage is when it pings, turn it back a degree.
Your carbs are probably in line with what I'm running. I worked out that 932s were about 25% more choke area than standard Shadow carbs so I started with a jet 25% bigger - 230, that seemed a bit weak so I'm on 240, and that seems near enough. I'd have tried 250, but I haven't got any, and the 260s I've got would probably be a bit high. Plug chops don't give much of a clue anymore, so it's down to easing the throttle down when pulling hard etc.
H
ps it runs nicely all through the range, docile and torquey at low revs and fairly rapid when the taps are opened.