Jaguar V12 engine misfiring? 1973 XJ-12 with original Jag. factory engine; 4 Stromberg carbs. with manual choke controls; automatic trans.?

Car has about 100k miles in coastal southern California, where it rarely gets below freezing nor hotter than 35deg.C=95deg.F. It starts and runs OK when cold (with the choke out two clicks, or three clicks in winter weather), then runs roughly on 9/10/11 cylinders for about 10 minutes while warming-up, wanting to stall. Adjusting the choke doesn't help keep it running at fast-idle, nor enable restarting if it quits. I have to aggressively keep it running using the gas pedal and left-foot braking, or park it for 10-15 minutes if it stalls. After the underhood/underbonnet space warms up (10-15 minutes), the engine usually runs fine on all 12 cylinders for the rest of the day, whether hot, cold, damp or dry, not needing the choke again until next morning. Sometimes it will revert to chugging on 11 cylinders for a few minutes (at any speed) while warm, then smooth out on all 12 again with no consistent pattern (seemingly unrelated to air temperature or moisture).

Easy stuff has been replaced: spark plugs, high-tension wires, distributor cap, rotor, coil, fuel filter, fuel pipes, vacuum tubing, thermostats (temperature gauge reads correctly), air filters, carburetor diaphragms, and more. Carb. intakes are set for a warm mix of ambient and exhaust-heated air. Fuel pressure for acceleration and high speed seems fine. Before getting into more difficult and expensive items like EGR valves and electronic ignition modules, I'd appreciate suggestions from classic car enthusiasts