[ROVERNET - UK] Adjusting Timing of 2000TC
magnet at roverclub.org
Sat Apr 5 00:25:03 BST 2008
Re North American 2000TC ignition timing, here is something I posted to
the 'net back in 1999. May still be useful information...
"Many years ago I had a North American spec 1968 2000TC, and
I recall it had a vacuum connection to the distributor that
seemed to work in the "wrong" sense. In other words,
rather than the vacuum providing additional advance to that
contributed by the centrifugal mechanism, an increase in
vacuum actually retarded the timing -- by about 6 or 8
degrees, I think it was.
This was intentional. These cars were early victims of the
U.S. emission control regulations, and the setup was
supposed to reduce emissions at idle, when the throttle was
closed. The idle mixture was supposed to be set
extremely lean, and in order for the car to idle
successfully on such a lean mixture, the timing at idle had
to be drastically retarded from the normal 6 or so degrees
before TDC to about 8 degrees after TDC.
This was done by using the vacuum unit on the distributor
to produce the necessary amount of retardation when a
vacuum was applied to the diaphragm. The vacuum
pick-off point in the carburettor was chosen so that there
would be high vacuum there with the throttle closed, but
much less vacuum with the throttle open -- in other words,
when you were actually moving. In the usual (i.e.
pre-emission control) arrangement, the vacuum pick-off
point in the carb was chosen so that the faster the engine
turned, the greater the airflow, and the more vacuum. This
then provided additional advance, except at very wide
throttle openings (such as during hard acceleration) when
additional advance would have caused pinking.
Although both the distributors and carbs on
the emission control cars were different from those on
earlier versions, the difference was not especially
obvious, unless you managed to figure out in which
direction vacuum would pull the diaphragm and which way
this would move the point mounting plate, and then sampled
the amount of vacuum at differing engine speeds.
I didn't think much of this arrangement, as it made
operation of the throttle anything but progressive. The
engine would come up from idle a bit slugglishly and then
pick up with a roar once the distributor regained its
proper degree of advance. I seem to recall disabling that
vacuum retard..... (tsk-tsk)"
With the vacuum retard disconnected, you can set the timing to about 3
to 4 deg BTDC and see how she goes. If she doesn't "pink", it's
probably a good setting and you can leave it up to the centrifugal
mechanism to provide the needed advance.
> I am wondering if it is worth adjusting the timing on my 2000TC. I
> remember from my UK days it being 6deg BTDC, but in the US / Canada
> the cars were set at 4deg ATDC, like my recently acquired TC. I think
> this is for emissions reasons to run on leaner mixtures. I am thinking
> that this US timing setting may make it harder to tune the carbs for
> smooth idling - am I right or wrong?
> 1969 2000TC
> 1970 3500S
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