One thing that would help you diagnose if this is an ignition issue would be to use a probe on the ignition wires in turn and look at the waveform on a scope. You could either use a laptop as a scope with a cheap usb scope online or you may have access to one.
The probe is for sale here https://www.aeswave.com/15-inch-Wyze...COP-p8764.html
Here is a guy using it on a car https://youtu.be/iFLaRd_5wc8
What you describe could also be attributed to sinking floats, have you weighed those ?