Pressure test-
Have you cleaned out the tank vent? If your not sure where its located, look on the schematic.
In order for the fuel to flow up to the carb, the liquid volume needs to be replaced by air. Additives in fuels mess with the plastic that the vent is made from. After the vent melts internally from the alcohol in the fuel, it wont pass enough air to keep the engine running. This may be the reason for the big bore kit to begin with?
Ignitions really dont have any parts that you can replace. When they get older heat bothers them. The internal capacitor seems to not be able to hold its primary voltage which makes it hard for the secondary spark voltage to overcome the Resistor in the plug. The R on the side of the plug has nothing to do with radio interference. The Resistor is in the plug to make the hottest spark possible for air pollution reasons. Pull the boot and look at the numbering on the plug. If you see an R, switch to a plug without the R like a regular CJ6 or CJ6Y Champion. Parts stores are used to handing out the R plugs so instead ask by part number. ngk? - BPMR7A? You want the non R which is BPM7A. So again no R plugs.
Are the carb diaphragms new?
On the pressure test your watching the gauge so you only have to disassemble far enough to get your gauge to work. For instance, you dont take the flywheel off unless your gauge indicates a leak or you see bubbles from soapy water behind it.