Jim,
Now you've got me confused. If your car has the vacuum pulled off the carb,
inside the butterfly (between the engine and the butterfly?) the vacuum will
approach zero as you open the butterflies and will build a negative pressure
as the butterflies close. The butterflies, restrict the flow of air into
the manifold, causing the vacuum to become greater. This would mean that
the vacuum would decrease with throttle, not increase, right?
Later,
Jack Brooks
1960 TR3A
1974 Norton 850 Commando
Hillsdale, NJ
> Perhaps the question really relates to where you are getting your vacuum.
> In my car the vacuum advance is pulled off the carb inside the
> butterfly so
> that vacuum and advances increases with throttle. The high
> manifold vacuum
> is blocked at idle by the butterfly. At idle advance is zero and goes up
> from there.
>
>
>
> Jim Altman jaltman@altlaw.com Illigitimi non Carborundum
> http://www.altlaw.com/metro/jaltman.html 69-TR6#CC28754L(O) W4UCK
>
>
>
>
> -----Original Message-----
> From: owner-triumphs@autox.team.net
> [mailto:owner-triumphs@autox.team.net]On Behalf Of Jack Brooks
> Sent: Friday, October 15, 1999 8:05 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
>
>
> > Jack :
> >
> > I'm not sure if I said one of those things that "just didn't
> sound right"
> > <g>, but I think Barry glossed over the point that most if not all auto
> > vacuum advance systems do NOT advance the spark at idle (unless
> the engine
> > is overheated). Efficiency at idle is not a concern (it's 0 by
> > definition),
> > and a retarded spark makes for a smoother, more stable idle
> speed. Also,
> > for most engines, the centrifugal advance is no longer working
> at idle, so
> > the idle timing needs to be retarded for the slowest possible speed, not
> > just the nominal idle speed.
> >
> > 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: Thursday, October 14, 1999 2:23 PM
> > > To: Triumph List
> > > Subject: Vacuum advance - Clarification
> > >
> > >
> > >
> > > A few days ago I was following a few posts about the way a
> > > vacuum advance
> > > works. Some of what was said, just didn't sound right.
> >
>
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