[T3] CDI Marathon!

Keith Park topnotch at nycap.rr.com
Fri Feb 5 18:35:02 PST 2021

I saw your ad on the Samba.  Im running a Mark 10 that Jim sold me, cleaned
up the ignition so that the cruise control works properly now, makes the now
Lubripoints last A LOT LONGER.  

I recommend them, just be careful... they put 400V on your coil B+  :-0


Topnotch Restorations
topnotch at nycap.rr.com
71 Squareback  “Hothe”
65 Notchback  “El Baja Rojo”
93 RX7  “Redstur”
13 Subaru Outback "Blendin"

-----Original Message-----
From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
Behalf Of Jim Adney
Sent: Friday, February 5, 2021 10:22 AM
To: type3 at vwtype3.org
Subject: [T3] CDI Marathon!

CDI stands for Capacitive Discharge Ignition, and I've been using Delta Mark
10 CDI units since 1966. That started out on Dad's Corvair and then moved to
my '68 Square. They install easily and work with standard points and coils.
I've been so pleased with their performance that I've bought and built (they
were available in kit or factory assembled form) several, but in recent
years, I've managed to buy several on ebay, when they come up.

This past week, I finally got around to testing a BUNCH of them. I clean,
inspect, and bench test each one, then repair and resolder as necessary. 
I've replaced all the rusty screws with nice stainless ones. When I'm
satisfied that one is good to go, I run it on the bench for at least an hour
and a half, at rates equivalent to 3000-12000 RPM. Now I've got a BUNCH
ready to sell. 
I've written up more on thesamba, where you can go to see pictures of some
of the ones I have available, as well as the instruments I use in the


Delta eventually made 3 main versions of this CDI: Mark 10, 10 B, and 10 C. 
I've never had my hands on a 10 C. The Mark 10 is a basic unit that will do
everything you need. The 10 B has slightly different internal circuitry, but
the only important difference is that it has a switch to change from CDI to
conventional. The switch is convenient, but they sometimes cause trouble and
need to be "exercised" to regain good contact. I make a point of exercising
mine any time I have the rear hatch open. This has eliminated any annoying

I have Mark 10s in 6 V and 12 V versions, negative ground.

Mark 10 Bs only came in 12 V negative ground.

CDIs give a hotter, higher energy spark that happens in a shorter period of
time. This reduces erosion (wear) of the spark plug electrodes. Plugs last 2
to 4 times longer.  

The CDI unit uses the points to trigger the discharge, but that trigger
current is small and non-inductive, so the point contacts last forever. The
only reason to replace the points is if the rubbing block wears too much or
the wire fatigues and breaks due to the flexing. My points tended to last at
5 years, even when I was driving a Squareback every day. Keep a tiny bit of
sticky grease on the distributor cam to lube the rubbing block.

If you've replaced your mechanical points with one of the electronic points
replacements, the Delta Mark 10s will also work perfectly with those.

But, let me be clear: If your current ignition system is running well,
upgrading to a CDI won't give you any more horsepower. There is nothing
magic here. 
If there are weaknesses in your high voltage components, the higher voltage
and faster rise time of the CDI is likely to find them and force you to fix
OTOH, that's what you should do anyway.

What you can expect is smooth running, reduced maintenance, and, possibly,
easier starting in very cold weather.

thanks for reading,

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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