1973 Beetle Type I DVDA Vacuum can test

[hercdriver]

I'm checking out the health of my DVDA before I start up my type I that has been rebuilt and waiting for break in. I'm primarily interested in testing the vacuum can to ensure that it wasn't part of the reason the car was left for dead so many years ago.

On a regular SVDA can, you can suck onto the vacuum port and watch the control arm move (it should also hold it's position until the vacuum is released).

Is the DVDA test the same, but only applied to both vacuum ports? Should you apply vacuum to both ports simultaneously? Should they both hold vacuum?

I'm also not sure where the lower vacuum hooks up. The upper port has a hard line to connect to the left side of the carburetor.

Here are the specs I plan on using for tune up. (it's an autostick)

1973 Beetle

VW distributer number 113 905 205AH
Bosch Parts Number 0 231 167 053
Vacuum Advance 113 905 271G
Timing 5* ATDC (vacuum hoses connected) at 900 RPM
28* BTDC at 3,000 RPM
Point Gap .016

[hercdriver]

I did find this on vacuum lines.

Flat side of can (retard side) connects to "On the rear (RIR) of the carb should be a fitting up towards, but not on the carburetor top." with 4.5 mm green hose.

Rounded side of can (advance side) connects to "The fitting on the LEFT side of the carb" with black 3.5 mm hose.

reference...
http://www.type2.com/library/electrip/dvh.htm



I'm still looking for a vacuum can test procedure.

[Amskeptic]

I'm still looking for a vacuum can test procedure.

Grab a hose that fits snugly on the retard nipple, and suck. You should see the lever push out. It should hold a vacuum. Same with advance side, except that the lever should pull in. That's it.
Colin

[Bookwus]

Hiya Dave,

Not that this matters a great deal........but..........your 205AH distributor is OEM for a 1972 set-up. In 1973 the stock AS (federal) dizzy was a 043 905 205A. The 205A wanted to be timed at 7.5* BTDC.

Make sure that your advance hose is hooked up to the vacuum port on the left side of the 34PICT3 AND that it has a high point (this is usually accomplished via the use of a hard vacuum line) higher than the vacuum port on the carb. The retard hose goes to the rear vacuum port at the 10:00 position relative the blow-out plug.

[Amskeptic]

The 205A wanted to be timed at 7.5* BTDC.

You don't even ask the distributor. If the distributor *has* a dual vacuum can on it, it *is* going to be timed at 5*ATDC. If anyone should time a dual advance distributor to 7.5* BTDC when the retard is working, you *will* melt that sucker on the highway.

Every Volkswagen distributor must be timed to 28* BTDC @ whatever rev is recommended (somewhere in the 3,000s), then you can see what is happening at idle when you get your hoses back on.

The retard spec that you see sprinkled in the tables, is strictly trying to meet the requirements of the carburetor. On cars with 7.5* BTDC, you can be pretty sure that it is a single can vacuum advance unit installed on the distributor and the carburetor is a low-flow throttle bypass. On cars with the 5* ATDC, the carburetor had best be the high-flow throttle bypass. When it is all working and adjusted, the 5* engines have robust idles that keep the exhaust system nice and hot and can handle auto-stick loads nicely.

My question for you Bookwus, is do you have any technical information on autostick clutch vacuum valves as they relate to timing specification?
The 7.5* BTDC engines will have higher vacuum 12-15", the 5* ATDC engines will have lower vacuum 10-12" and would this affect valving?
As represented in different part numbers or anything?
Colin

[Bookwus]

Hiya CK,

During the eight plus year production of AutoSticks VW changed the distributor a number of times. Timing specifications from the factory varied from 5*BTDC, to TDC, to 7.5*ATDC. During that production run the control valve was changed (modified) only once. And that was to accomodate changes needed with the introduction of FI in 1975.

FWIW, the control valve was equipped with an adjustment screw. This made the control valve either more or less responsive to the vacuum signal received from the intake manifold. I'm guessing that said adjustment screw compensated for differing levels of vacuum with the differing distributor set-ups.