Chris, a while back you composed the following response (at the end of
this message) to Cory regarding pinging, timing, distributors and Weber
downdraft carbs. I have a couple of questions, I was wondering if you
could address them?
Does your information about vacuum advance (on the DVG) only effect idle
timing, and not the 3000 rpm ping?
I've got the ping.
How do you choose lighter springs? As I remember the mechanical advance
springs in my distributor are two different weights now, one is very
light, one is very heavy. Wouldn't lighter springs allow too much
advance and increase ping? If I've got this right you retard timing to
eliminate ping. The problem I have is if I retard enough to reduce the
3000 rpm ping then the car runs like crap.
What if I eliminate the vacuum advance on the Lucas dist? Would the
mechanical advance be all I need?
How about the Mallory Distributor? In a previous post you write:
"I would suggest the mallory electronic ignition distributor and
performance coil. It's the same
as the dual point distributor you see in vicky brit but it has a mallory
unilite electronic ignition unit in it instead of points. Available from
Summit, it was cheaper than buying the dual point from vicky brit and is
more reliable."
I assume that if I ever put a Weber DCOE (got one in my garage somewhere)
that the Mallory distributor would work for that too.
Thanks for any help.
Cheers,
Larry Hoy
1969 MGB Roadster
1987 Jaguar XJ6 Vanden Plas
1976 MGB Parting out
================================
>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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