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Re: Cams and Distributors

To: CREICHLE@nsc.msmail.miami.edu
Subject: Re: Cams and Distributors
From: larryhoy@juno.com (Larry A Hoy)
Date: Thu, 13 Feb 1997 15:55:57 EST
Chris great information, thank you.  I have experianced the same
situation that Corey has. 

Cheers,
.
Larry Hoy
1969 MGB Roadster
==========================
On Thu, 13 Feb 1997 09:50:00 -0800 (PST) "REICHLE, CHRISTOPHER"
<CREICHLE@nsc.msmail.miami.edu> writes:
>
>The vacuum advance only brings in advance when there is vacuum ie when 
>you are at part throttle or idling. If you want to hook it up you should

>tap a hole in the weber manifold closer to the carb if you have the
option 
>otherwise shock waves from the valves closing will influence it. The 
>ported vacuum on the DGV is above the Butterfly plate and will appear to
work 
>fine except at idle where it will look to the distributor like you are
at 
>full throttle with no vacuum. Tap the hole and insert a fitting. That
will 
>save you some gas and allow you to lower your idle speed adjustment
which 
>may help any runon problem you have. At idle, the fuel air mixture is 
>burning so slow that 15 to 20 degrees advance may be added by the vacuum
>advance unit.  Adding 15 to 20 deg advance with the vacuum advance unit
will raise 
>your rpm a bit and you will have to turn down the idle adjustment a bit.
The 
>net result is that you are using less gas at idle with the vacuum
advance 
>unit active and the likelyhood of runon after ignition shutoff under
these 
>conditions is less likely.
>
>The reason your not jumping off the line against those minivans (aside 
>from the obvious...) is that you probably do not have enough advance at 
>lower rpm. To test this, set your distributor a few degrees more
advanced. 
>If you feel a little more power off the line you needed more advance at
lower 
>rpm.  The only problem is that now you probably have a ping up around
3000 
>or so because your mechanical advance is still adding advance. Lighter 
>springs would bring the advance in quicker and allow you to maintain
your 
>current timing at 2500 but increase the timing advance in the lower
rpms. I 
>originally was going to write a detailed explanation of how and why to 
>do this but as it amounted to over a page and a half of dry reading I 
>decided  to give you the option of taking my word for it or replying me 
>directly for more info as to not bore the list (like I haven't done that
already...). In >between my responsibilities at work it was also taking a
few days to 
>finish.
>
>Chris Reichle
>creichle@nsc.msmail.miami.edu
> -----
>From: mgs-owner
>To: mgs
>Subject: Re: Cams and Distributors
>Date: Tuesday,February 11,1997 1:25PM
>
>Chris, friends, etc:
>
>I've got a very similar set-up on Rags: 79 engine, header, free-flow
>exhaust. However, I've got a Lucas 25D dizzy on the engine ... one 
>from
>an older (pre-75) MGB.  I've got a Weber DGV 32/36 carb on the car.
>
>Right now, I've got the vaccuum advance on the distributor closed off,
>idle advance set at 15deg BTDC @ 1500 rpm.  I'm not interested in
>replacing the cam.  Two questions:
>
>1) Has anyone any experience with changing the idle advance, and what
>are some good settings? Rags is pretty happy with 15 deg, but I lack
>power on takeoff (witness being smoked by a minivan last week).
>
>2) If I were to attach the vaccuum advance to something, does anyone
>know where on the DGV it should go? And what might be the practical
>advantages of this?  Rags has pretty good power from 2500 rpm to 
>around
>4800 or so, when it starts to level off.  I usually shift around 3800
>or so in normal traffic.
>
>Thanks!
>
>Corey
>75 MGB 'Rags'
>

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