Classic cars forum & vehicle restoration.

[Miken]

I bought a nice 1954 Austin A40 Devon a couple of Weeks ago.
I've been giving it a bit of a service.
I have now obtained the correct original Austin manual that says that
"The correct ignition timing if using standard fuel is 7 degrees btdc and, for premier fuel 10 deg btdc".
So, my question is, which of these would be good a starting figure using modern unleaded (I don't know what old fashioned standard and premier petrol was equivalent too).
Or am I likely to need more or less advance than either of these figures.
Thanks
Mike

[alastairq]

The important thing is the octane rating.

Current ordinary petrol [leadless] is 95 octane.
This is equivalent to the 60s'/70's 3 star petrol. [IIRC?}

Super unleaded usually is 98 octane [Tescos os good apparently]
Some branded super fuels are over 100 octane.

I think the old 2 star petrol [cheapest in UK] was 91-92 octane.
I think Pool petrol was 85 octane [Ford sidevalve engines would run happily on this]

However, there is the added nuance of the fact that today's petrol burns at a far higher temperature than, say, 80's unleaded fuel.


Not an issue for modern engines, with their knock sensors constantly fiddling with their ignition timing.

But For carbs and dizzies, could be a nightmare?

Best to start with around the lower figure for static timing..then get experimenting on a known road [with a bit of a gradient helps....loads the engine] and do some acceleration runs....keep advancing the dizzy bit by bit until you can just hear the pinking noise when pulling hard..then back off the timing a tad.

Or, pay someone on a rolling road to do it for you?

Once you have the near optimal settings, mark dizzy or timing marks appropriately.

Remember, the manuals were written [note, not printed?] ata time when petrol was a very different beast. So most older petrol engines will benefit from having their timing adjusted a bit,here & there....also takes note of any inherent wear in the engine?

The Americans [bless 'em] like to do all this with a vacuum gauge....using manifold vacuum.....sets idle mixtures, and initial timing points, to a treat.

Th e point I'm making is, the factory figures are a starting point, not the be-all-&-end-all?
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[Penman]

Hi
I would think that the "Standard" fuel back then was quite a low octane, Pool petrol might still have been available round that time and that was about 72. I doubt anything would have been available close to our current 97RON Premium fuels.

I'd stick with their premier fuel setting.

Rick ought to know he has had Devons.
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Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10

[alanb]

My Morris 8 runs best using the lowest grade of petrol and advancing the ignition timing by about 5% more than the manual suggests. The simplest way is to gradually keep advancing the ignition until the engine starts to "Pink" under load, then retire a couple of degrees until it stops pinking. You may then need to adjust the mixture to obtain smooth running.
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old tourer


Morris 8 two seater

[Miken]

Thanks for the interesting replies.
As soon as I get my distributor back from the Distributor Doctor I hope to try it out properly.
Anyone who thought that Austin stopped making Devon saloons in 1952 is correct. Mine is a pick up truck which continued in production for a bit longer.

[Rick]