Stuart, I had totally random cutting out issues with my T160 Trispark, sometimes doing 40+ miles before the fault recurred.
I made two alterations recommended by Steve Kelly, and don't know which of the two alterations cured my problem, as I did them both at the same time. I put resistor plugs on and moved the remote black box away from the coils,rearwards a few inches. No more problems.
I have had a problem with my Norton Trispark this year. I had intermitant total failure of the ignition system and also momentarily cutting out. I sent it back to Steve who replaced it with a new one with a modest financial contribution from myself. Steve did say that on his tester that no fault could be identified, but that intermitant faults are difficult to find.
The new one sorted the problem and I am very pleased with it and the aftermarket service supplied by Steve.