Check the fuel pressure, it should be 4 bar / 60 psi on a twin cam.
Mine was down to 30 psi under hard acceleration and recording an afr of 18 to 1 so was struggling top end ( if I had carried on it would have been by-by valves).
The pump had done 42K miles.
The pressure regulator is mechanical and there is no sensor to let the ecu know the pressure is low.
At full throttle it is in open loop so the lambda sensors can`t try to compensate for the lean condition.
I will factor this in and now try see what i need to measure that as that sounds about right.

