Just went out and looked CAREFULLY at my SUs on my stock
The vacuum comes off a nipple just about in the center
of the intake manifold.
There are NO unused nipples on either (or both) SU base.
The only likely ports are for the Y hose to the oil separator
for PCV use.
So where should I drill and tap for a nipple? Front or back
SU? At the base? On the manifold side of the throttle body?
David Riker wrote:
> Actually, the correct place on the SU for the vacuum advance is a throttle
> vacuum port on the carb. If you are drawing manifold vacuum you have the
> hose hooked up in the wrong place. On the SU, the vacuum provision is
> exactly like what we've been trying to duplicate on the weber.
> 74 Midget
> 63 Falcon
> ----- Original Message -----
> From: Richard Shipman <firstname.lastname@example.org>
> To: David Riker <email@example.com>
> Cc: <firstname.lastname@example.org>
> Sent: Wednesday, August 04, 1999 5:50 AM
> Subject: Re: Timing the 1275 ? (vac. advance with a sidedraft)
> > Can anyone explain to me why my '74 Midget with SU's has a simple vacuum
> > advance fitting right on top of the intake manifold and yet so much care
> > attention is being taken to locate the vacuum pick-up at a specific point
> > a sidedraft weber??
> > What am I missing??
> > Thanks in advance
> > Richard
> > '74 Midget
> > '68 MGBGT
> > '58 Morris Minor
> > At 09:54 PM 8/3/99 -0700, you wrote:
> > >Bryan:
> > >
> > >Just went out and took a good look at exactly where I drilled the hole.
> > >took me two tries to get it right. The spot is at 11:00 on the front
> > >throat, and goes through the bore only a few thousanths in front of the
> > >butterfly. Too far away from the butterfly and there won't be enough
> > >to opperate the advance. The choke (enrichment hole) is a few thousanths
> > >after the butterfly and would be subject to vacuum at all times. If I
> > >understand vacuum advance correctly, it's purpose is to improve fuel
> > >under light load only, like at highway cruising speeds. At Idle, an
> > >has to have minimal advance to prevent backfiring and hard starting.
> > >Centrifugal advance corrects the timing necessary as engine RPM
> > >and Vacuum advance allows the timing to advance or retard based on engine
> > >load (how am I doing so far?) On a race engine, you would be under load
> > >most of the time, so vacuum advance wouldn't be necessary (hence Cooper
> > >Distributors with no vacuum advance provision). Manifold vacuum will not
> > >work correctly because manifold vacuum is too high at idle and under
> > >acelleration, resulting in timing that would be too far advanced in both
> > >those situations.
> > >
> > >That is how I understand it, anyway. My fuel economy improved about 4
> > >highway when I hooked up the vacuum advance.
> > >