So, once again, Bob IV hasn't been well. Quite apart from the clutch pedal failing a week ago (which makes your gearbox lock up when you stop), there have been intermittent misfires. Not helpful when you need to accelerate, only to find that you make a noise reminiscent of the
Bulletproof Bomb.
Still, following some expensive repair work, there seems to be a solution:
Honestly, I don't know why I didn't see it earlier. I mean, just look at it. Tchoh.
Okay, according to the garage, this is a close up of one of the valves on the number three cylinder. It's become contaminated and burned, preventing them from sealing properly, which means that eventually the whole engine cycle just temporarily gives up and stops firing 25% of the time - I'm learning new stuff all the time!