Jack :
Ducking (for the moment) the issue of whether "most cars do" or "most cars
don't" <g>, I can say with certainty that the stock setup for your TR3A :
1) Uses 'ported' vacuum for the vacuum advance, which means little or no
vacuum is applied to the advance unit at idle. Once the throttle is opened,
the advance unit essentially sees full manifold vacuum, which is high under
light load, and low under heavy load.
2) Has only a vacuum advance, which means the ignition is advanced when more
vacuum is applied.
BTW, point 1) is easy to demonstrate : disconnect the advance line with the
engine idling (normal idle speed), and cap the end with your finger. If the
advance was active, the engine speed will slow dramatically (or even die).
Since the advance isn't active, it actually makes no difference whether you
cap the line or not, the engine speed stays the same.
Randall
59 TR3A daily driver
> -----Original Message-----
> From: owner-triumphs@autox.team.net
> [mailto:owner-triumphs@autox.team.net]On Behalf Of Jack Brooks
> Sent: Friday, October 15, 1999 5:05 AM
> To: Randall Young
> Cc: Triumphs (E-mail)
> Subject: RE: Vacuum advance - Clarification
>
>
>
>
> Randall,
>
> The bottom line is that at idle, the vacuum advance is pulled
> in by the high
> vacuum in the inlet manifold changing the timing. When you open the
> throttle, you let in more air and bring the vacuum in the
> manifold closer to
> zero, allowing the vacuum advance to move back to it's static
> position. So,
> the question is whether the engine is advanced or retarded as
> the vacuum
> decreases or increase.
>
> Listers, can anyone shed some light on this issue?
>
> Thanks,
>
> Jack Brooks
> 1960 TR3A
> 1974 Norton 850 Commando
> Hillsdale, NJ
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