My '63 +4-4Str also has a TR4 engine. I wash it at the Car Wash regularly. No Problems for Me. But I have had a rash of coil problems. Last time was in Southampton, UK when +4 just stopped. Flat Bedded to a local mechanic who changed the coil to a Lucas coil. I think I had a Bosch Blue. OK since then. But I do carry a spare coil. I also replaced a Pertronix Electronic gizwiz with a new Lucas Dizzy with Points. Of course I also have a spare set of points, rotor and cap. As I was into the ignition anyway I made up MSD ignition wires. I also have quit using those cheap insulated connectors and crimper and now us un insulated connectors and a much better (more expensive) crimper. (same system used by Kit Airplane builders).
As a general rule it will not be the SU Carbs that are faulty, but will be the ignition.
