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The Vintage Sports Car Club of Australia
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The Vintage Sports Car Club of Australia
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Tuning Noel's Derby Bentley |
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I recently tested my Derby on a dynamometer
in Sydney. I was concerned about the car
running too lean at my cruising speed of
60mh with 3.6 diff. Recent stories from the
UK about burnt pistons because of lean
running finally persuaded me to do the test.
The standard AW needle showed Air/Fuel Ratio of 16 at 3000 rpm - too lean.
Tested needles C and 6. No good.
Fitted BU needles and did 2500 km
return trip to Brisbane. Plugs were
very black.
Changed BU for S5 and now engine seems
to be very good. Under high cruise AFR
is 13.7 and hard acceleration shows
12.5.
My engine is 5000 miles since a
complete overhaul and is standard.
I fitted new BP6ES, new points and
set tappets to .004 & 6". SUs in
good condition but interesting to
measure one dashpot 7gms heavier
than the other, which was corrected.
Test done at sea level, 19C,
1013mBar, 60%humidity. Used
standard Unleaded, 0% ethanol.
Noel
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