Lee,
I quote the Haynes Manual, "Normally an engine will idle on only a small
amount of fuel/air mixture. It is very difficult to ensure this is just
the right proportion to meet the emission requirement, and so there is
risk of too much carbon monoxide (CO) in the exhaust. Therefore the
ignition is retarded later than the timing that would give the best
idle; so the throttle must be opened more to keep the engine speed
satisfactory; this greater flow through the carburetor can be kept to
the required fuel/air proportion to minimize CO. To do this the type
D204 distributor has a double acting vacuum mechanism."
So to put it more simply, to reduce emissions at idle. Later models
dropped the advance altogether.
Joe
Janssen, Lee K wrote:
>
> Could someone explain why the early model TR6s had both a vacuum advance AND
> retard??
> Thanks for the info.
> Lee Janssen
> Denver CO
--
"If you can't excel with talent, triumph with effort."
-- Dave Weinbaum in National Enquirer
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