From the horses mouth = approved, accredited, authenticated, direct, primary source, trustworthy, dependable, etc etc; basically the best source anyone can get.
Pool petrol was way lower octane than anything we have now, so if engines were finicky then one would expect to go leaner. However at something around 5 to 1 compression an engine is said run happily on a 20% paraffin mix [there's a scale chart for this based on compression] that probably equates to pool petrol. Thus any changes needed are more likely to come down to the relative viscosity.

Sorry Jeremy, I still have to learn colloquial language a bit better!

The settings of 1939 were likely not yet based on pool petrol I would think but I do not know when that was introduced.

email (option): wd16h@telfort.nl

In my experience [I got invited over to a National Klompen festival] the Dutch speak far better and more correct English with a wider vocabulary than the vast majority of my townsfolk.
As for pool petrol [74 octane] the only interweb date I've found is 1/1 39, earlier than I thought. I think it persisted until 1952 and yet carb specs didn't subsequently change, although compression ratios went up on subsequent ohv models. Of course all that was petrol, of a sort, not the chemical concoction we have now.

On the website of the Cornwall Austin 7 Club, (http://pub37.bravenet.com/forum/static/post.php?usernum=3155626639&frmid=16&msgid=1469300&cp=0&reply=1469300&mode=add) is a fairly elaborate description and timeline of the events leading up to pool petrol.
It actually started in September 1939 and had an average of 74 Octane as you also mentioned.

email (option): wd16h@telfort.nl

According to the "Flimsy" cans is was 80 during the early part of the war. Ron

email (option): ronpier@talk21.com

The Hansard of November 1950 shows a statement in the UK government as follows:
"Before the war we had three grades of petrol — commercial 68 octane, No. 1 grade 75 octane and top grade 80 octane. I am advised that very few vehicles used 80 octane. Nearly all of them used the other grades."

This was an answer to the question whether the standard could be raised to 80 Octane.

See https://api.parliament.uk/historic-hansard/commons/1950/nov/13/pool-petrol-standard

This suggests that 80 was indeed reduced to a lower Octane value due to production output limitations.

Cheers,

Rob

email (option): wd16h@telfort.nl

Given the above I rather doubt pool petrol even reached the heady heights of 74 in the latter part of the war. I would think it was reduced to the lowest that engines would tolerate. It certainly had a pretty poor reputation. There were plenty of profiteers around to water it down, probably with paraffin. Records are just that, not always reality.....

Having run out of any definite information in my files, I have only references to "Standard", I have resorted to Google. I've found a number of forum posts by Phil Beresford who is referred to as "Technical Sales Co-ordinator" At Burlen Fuel Systems.

The earlier link gives more detail. He states that the Standard was 1065, but it is no longer available and is commonly replaced by a 106.

https://www.britbike.com/forums/ubbthreads.php/ubb/printthread/Board/2/main/41824/type/thread

In the second link, he again categorically states that the standard for the 276 was 1065.

https://www.britbike.com/forums/ubbthreads.php/ubb/printthread/Board/1/main/76201/type/thread

So it seems that at some point, either under Amal or Grosvenor Works who took over from them..or maybe even Burlen, the 1065 was discontinued and only a 106 supplied, for reasons that we don't know...Did it work better ? Could the change even have taken place in the 1950s prior to the Monobloc appearing?

Whatever, although there is no stock listed on the website, it seems that they are in production again.

It's possible that Nortons were used in the 276 testing and that was why the half size ended up as the unmarked standard. The 16H was at the end of the 1930s the most produced model in Britain. Norton were making little else and, like Hawker with the Hurricane, may have been turning out as many units as they could afford prior to the Ministry actually ordering them. Both Amal and Norton were based in Birmingham.

Pursuant to the above Wiki states that Monoblocs use of idle jets meant they just had one standard jet block, and that that was a significant change from pre monoblocs, simplifying production. So it's very possible that a new [or even just later] carb set up for a 106 would not work as well with a 1065. My carb is however a war era one.