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RE: Vacuum Line 1275

To: "'Mark Endicott'" <endicott@bellsouth.net>, "'Spridgets'" <spridgets@Autox.Team.Net>
Subject: RE: Vacuum Line 1275
From: "Seippel, Jim J" <Jim.Seippel@siemenscom.com>
Date: Mon, 19 Jan 1998 08:47:32 -0800
Reply-to: "Seippel, Jim J" <Jim.Seippel@siemenscom.com>
Sender: owner-spridgets@Autox.Team.Net
No, No, No! 

The vacuum advance port on the carbs is in front of the throttle
butterfly. This means at idle, you have little or no vacuum and as you
open the throttle, the vacuum will increase thus increasing the advance.

If you use a port on the intake manifold, you will have a large vacuum
at an idle when the throttle is closed. As you accelerate and open the
throttle, the vacuum will decrease. Therefore, you will have a large
advance at idle and the advance will decrease if you accelerate. This is
not what you want unless you have a distributor with a vacuum retard.  

I found this problem on a '67 MGB after a friend of mine had performed a
lot of work trying to correct a problem with a lack of power and
overheating. He had the advance port on the carb, but had blocked it off
because the metal line from the vacuum advance was too short and it
reached the manifold easier. The timing was set at 5 degrees BTDC
statically. When the engine was started, the timing was about 20 degrees
BTDC. At about 3000 RPM the advance was back to the 5 BTDC. If he set
the timing at idle to 5 BTDC, he would up with about 15 ATDC at 3000
RPM. 

The best fix is to use a mini-cooper distributor which uses a mechanical
advance and does not have a vacuum advance. Another fix is to use the
weights and springs out of a mini distributor to rework your
distributor. 

Best regards,

A.J. (Jim) Seippel
jim.seippel@siemenscom.com

"Age and cunning is always better than youth and enthusiasm"

>-----Original Message-----
>From:  Mark Endicott [SMTP:endicott@bellsouth.net]
>Sent:  Sunday, January 18, 1998 11:31 AM
>To:    Spridgets
>Subject:       Vacuum Line 1275
>
>I am in the process of installing a rebuilt set of SU's on my car and
>ran into a little problem.  The vacuum line was attached to the front
>carbueretor on the originals.  The rebuilts that I have don't have
>this port. I see that some earlier cars had the vacuum line attached
>to a port on the intake manifold.  My manifold has a plug (screw) in
>this hole.  Is there any reason not to connect a brass nipple to this
>port and use it for the vacuum advance?
>
>TIA
>-- 
>Mark 
>WB0NOO
>1970 MG Midget 
>S/V Witchcraft,S2-27
>Nashville, Tennessee

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