[Mg-t] MG

[Richard Lindsay]

Len asked, in a private reply, if today's Moss distributor springs, and
therefore the ignition advance curves, were updated for today's fuels. I
reply to all, since other may be interested.

Hi Len, et al.,

No, they are the same stiff springs as original. Further, the two springs
are the same so the curve has no 'knee' in it, unlike the profile used by
Jaguar in the 25D6.  Or is it a 45D6? No matter, the concept is the same.

Today's fuel with 10% alcohol contamination, affects more than just the
advance curve.

+ There are typically no rubber hoses in the TD fuel system but some of us
have added filters,  including me. If so, that rubber hose needs to be
alcohol safe. e.g., don't use ages-old hose you found in the bottom of a
garage box. Alcohol attacks old compound 'rubber' hose.

+ My SUs are rebuilt with modern kits but I don't know how well the
'glands' or seals on the jet tolerate alcohol. I am watching for leaks.

+ Pure petrol has a 14.7:1 air:fuel ratio, by weight, for complete
combustion. Maximum power happens closer to 12:1 (a little rich). Ethanol
has a 9:1 air:fuel ratio so adding in 10% of that stuff (to the fuel, not
the driver) upsets the ideal composite air:fuel ratio. Modern cars with
lambda feedback loops, simply adjust the charge mixture via the engine
management system. Old cars, anything pre-oxygen-sensor, perhaps should be
adjusted by us, for the fuel being used.

+ For my fellow nerds, alcohol has oxygen within its structure, so less air
is required. Reference:

http://www.brighthubengineering.com/machine-design/15235-the-stoichiometric-air-fuel-ratio/

-rick
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