canada wrote:
>
> Fellow Listers:
>
> Why does the Bentley manual and most other specs I've read call for
> setting the idle timing of a 76 TR6 at 4 degrees ATDC when my car runs so
> incredibly well now that i've set it at 12 degrees?
>
> At 4 degrees, the engine stumbles and misses terribly after it warms
> up--the subject of several recent postings and hours of lost sleep.
I would suspect that your car has some nonfunctional vacuum tubing
or diaphragms in the vacuum retard circuit.
"Late" cars with vacuum retard units operating from manifold
vacuum had these "late seeming" ignition timings.
Basically, at idle, manifold vacuum is very high, so the vacuum
retard unit is fully retarding. With retard fully on, 4ATDC is
a reasonable setting. When you open the throttle to start the
car in motion, the vacuum retard stops retarding and the ignition
timing goes to about what you'd think.
With a fully functioning system, a car with vacuum retard
set to 4ATDC at idle and one without set at 10BTDC at idle
work out about the same for the running range.
If you set your car to 4ATDC and the car runs crappy, it
is likely that your vacuum retard circuit is missing or
nonfunctioning. So you actually ARE running a really late
setting during running, not just at idling like it should.
Check the system, or... don't bother, but understand that
is where the bentley manual is coming from, a fully original
car in full operation.
--
Trevor Boicey, P. Eng.
Ottawa, Canada, tboicey@brit.ca
ICQ #17432933 http://www.brit.ca/~tboicey/
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