When they're good, they're very very good

But when a bike breaks down they're fucking awful.

Get up at sparrowfart this morning, for a 6 o'clock start at work. On
bike and trundle off. Get onto M4, and it loses power and cuts out.
Coast onto hard shoulder have a quick check - fuel O.K., as I can see
into the newly fitted inline filter. Prod the starter and the bike
coughs into life, albeit running on 3 cylinders. Blip the throttle a
couple of times and it clears its throat. Back on and away we go.
Except, after about a mile, the bike cuts out. Coast onto hard
shoulder, check the exhaust headers - yup, definitely running on 3.
Scratch boll^Whead, try starting - yes, but still on 3 cylinders. One
final try to either get to work, or, turn around at the next junction
and head home. Yes, you guessed it, repeat the cut out, coast, stop
process. Except this time, it's time to give up and, for the second
time in 2 weeks, call Auntie Carole's breakdown service.

Watch the sunrise over the Severn Estuary, which was nice and wait.
Give the bike another chance and this time, the awkward little sod
decides that it'll run on all four cylinders. Bloody thing. Breakdown
bloke turns up - small recovery truck with a bike trailer on the back.
Bike onto trailer, strapped down and recovered to home.

Hopefully, all it'll need is a new set of spark plugs or at worst the
CDI unit's fucked. Any other suggestions, apart from get rid of the
fucking thing?

 

If it's just one pot it's unlikely to be the CDI, or the coils, or
indeed anything expensive. My guess is a plug, plug cap or HT lead.

*Conceivably* the carb, but unlikely.