Aye Propeller,
Thank you for that gem.

The wee pins on the valve were that clarty, that they were jamming 'open', and therefore, a choking effect upon the engine when trying to accelerate into a headwind caused by excessive richness. Hence, the blubbering engine and unwillingness to respond to the throttle and rev' cleanly.
It would also explain the increased reluctance to start, when given 'choke', as the wee dodger would have been drowning it's cold plugs.
Needless to say the little rubber disc will be created and inserted in the orifice of each carb and the plugs over the idle mixture screws removed and the necessary adjustment made.
Whilst the Bros is a grand wee bike, shoe horning that V-twin into the 250 alloy beam frame makes access for maintanence diabolical.

The makers are often cursed in the terms used by HRH D of E, when addressing that other large Oriental nations populace, as I try to fit my Anglo Saxon mitts into another impossible position, whilst genuflecting beside the bike!

Slainte, Bill.