Why did it stop?
I honestly do not have a concrete answer for that! It has never stopped before and I have been through the fuel system checking filters, been through the throttle linkage for play and can confirm it still idles somewhere between 750 and 800rpm. I've checked the mixture at idle and it is a tad rich (safe). I actually checked the mixture was fully rich on Sat once it was stopped and I checked that the purge valve was closed, too.
I have convinced myself that as it wanted to depart to the right and I wanted it to go left - I turned it hard against the engine and gyroscopically stopped it.
Once I had it running again it was running very sweetly but figure 5 was a stall turn and I need to close the throttle again just as the rudder bites to stop torque overpowering aileron authority...you can bet that I pulled the power back very, very gently and gave a huge sigh of relief when it carried on running!
Funny old thing was that the sequence came with a recognised break point after figure two for Aerobats and Stampes - no penalty for breaking as Ludwig stated - I just zero'd the second 270 turn as my mind wandered back to the spin!
Ho hum.
Going to fly it again tomorrow (off for a meeting at Wellesbourne) then when I get home I'll run through the sequence a few times and do exactly what I did on Sat to see if I can recreate the problem.
Stik