IME electrical problems are load-related - it always gets better when you back off, worst at high speed and load, and worse in high gear than 1st gear.
Your mechanical advance may be sticking?
1 valve too tight, and not fully closed when hot?
The accelerator pump only works for the first small throttle travel distance, and then only for a few seconds. It will never go on and off, or occur at part throttle.
