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by John Connelly,
aircooled.net
Aircooled VW owners have an assortment of options when choosing a distributor
for their engine. If you only look on the surface it seems simple: The "obvious"
choice is the Bosch 009, right? Not necessarily. Once you do a little research,
you'll find a variety of stock units (including the SVDA unit), as well as the
Bosch 009, 010, and 050 series, and finally the Mallory, MSD, and the age old
Magneto. So which one is best?
Each
of these units is excellent - for the right application. In this article, I will
clarify the right time and application for each option available. You can read
the entire straight through, or skip directly to your area of interest using the
quick links below:
Stock Engines
"Old Faithful", the VW Stock Distributor (Vacuum Advance)
We
will start at the obvious place, which is the beginning. Up through the late
60s, VW supplied their engines with the stock distributor, which was a non-smog
distributor (emissions were not an issue). These vacuum advance distributors do
their job well, and all are dependent on a vacuum signal from the carburetor,
(with the exception of some early type 2s, which were chronically under-powered
and used a centrifugal only distributor). Stock units work VERY well when
installed in stock or near-stock engines with 28 or 30 series carburetors. Most
complaints are related to a defect of some sort (bad points, condenser, worn out
distributor), or a problem that is giving symptoms of a bad distributor, but is
actually fuel system related.
One
of these two modifications are the most common:
-
The carburetor is changed to something other
than stock, and it is almost always missing a vacuum port for the vacuum
advance distributor to operate properly.
-
The high performance engine does NOT have a
proper vacuum signal due to a long duration camshaft. Cam overlap will cause a
drop in vacuum, and obviously, the vacuum advance won't work properly.
The
010 Distributor
Bosch
came to the rescue with the 010 Distributor for early hot-rodders. This
distributor eliminated the vacuum advance system, and used ONLY engine rpms to
dictate the ignition timing. For high performance engines of the time, this was
the perfect solution, since these engines were usually run at idle or full
throttle!
The 009 Distributor
In 1971 (in the USA) the VW engines were shipped with a "smog" distributor,
which had a vacuum retard in addition to the vacuum advance. The engines were
also changed to the dual port configuration, along with a change in carburetors
from the 30 PICT series to the 34 PICT series, which had the additional port for
the vacuum retard. These new carbs were also LEAN in their operation, since they
had to conform to the new tailpipe standards.
The 009 distributor was introduced, and was a very inexpensive "replacement"
unit for VW engines, and it was almost a duplicate of the earlier 010
distributor.
These 009 distributors were (and still are) sold by the ton. Early VW engines
(pre-71') had no problem, but the smog engines when equipped with the 009/010
distributors had a pronounced and annoying "flat spot". A "flat spot" is a
hesitation just off idle, and can range from being almost unnoticeable to
getting broad-sided or rear-ended by approaching cars! (Many 009/34 equipped
owners mistake this hesitation for POWER. They don't notice the hesitation, but
they DO notice the kick in the back of the seat once the engine catches and it
starts accelerating! They mistake this for "more power" since there is such a
difference between the stumble and actually operating properly.)
The vacuum advance distributors do not have this hesitation since they advance
the timing when the throttle is opened as part of their operation. Obviously,
the 009/010 is only rpm based, and this vacuum advance doesn't happen. When a
009/010 is combined with the lean SMOG operation of the 34 series carb, the flat
spot is the result. Current "solutions" are all modifications to the carburetor,
which richen up the fuel delivery in various forms, whether it's the idle
circuit, the main jet, and/or the accelerator pump circuit.
The error with these "fixes" is that they are curing a symptom, not THE PROBLEM.
The problem is the lack of additional advance just off idle, not lean operation.
The stock distributor/34 carbs didn't have a hesitation!
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