Distributor Advance - '72 Super Beetle

[hambone]

Hello, I have a D/P type1 with a single vacuum distributor. I have timed it per specs (7.5 BTDC @ 900 RPM), and also marked the 30 deg. full advance on the pulley.
When timed at idle, and then the engine revved to high rpms, the timing does not advance all the way to 30 deg, it stops around 20 or so. To me, this indicates a distributor needing rebuilding - but I wanted to confirm here before I took it in. Sucking on the vacuum line does move the plate, but not as much as it "should".

Upon driving the car, there is the "009 flat spot", so this seems to prove it. Otherwise the car runs well.

Thank you! 24/48 hour turnaround at Philbin, so nice they're here.

[SlowLane]

Sounds as if your centrifugal advance is not giving you all it should. At high RPM with low load your vacuum advance wouldn't be contributing much.

Are you sure you've got the right distributor? My '72 Super had a dual-vacuum can, but maybe that was because it was originally an auto-stickshift. Have you checked your distributor model number against the Old Volks Home dizzy list: http://www.oldvolkshome.com/ignition.htm?

Either way, sounds like it needs some attention. Lucky you, having Philbin's in your back yard.

[Amskeptic]

Sucking on the vacuum line does move the plate, but not as much as it "should".

Define "as much as it should . . . "

The full centrifugal advance should be 28*. If you add all the vacuum advance allowed, it is only an additional 8-12*. Because the distributor is rotating 1/2 the speed (and distance) of the crankshaft, the vacuum advance unit should pull the breaker plate only 4-6*.
Science, my boy, science,
Colin
(p.s. the '72 engine had vacuum retard from the factory to allow greater airflow through the carburetor at idle with a 5*ATDC timing specification. If you have the oem Solex 34Pict3 carb with an advance-only distributor (7.5* BTDC), then you have to choke off the idle circuit to keep the idle speed correct . . . flat spot city)

[hambone]

It was once a dual vacuum distributor that was re-canned at some point to a single. Is this a vacuum only distributor? When did VW start with the SVDA stuff?
Yes the carb is a German Solex 34 PICT3. What would then be the best distributor for this combo?
Distributor: VW 113-905-205AJ, Bosch 0231 167 049 > 043-905-205C, 0231 176 028
Can Use: VW 113-905-205AN, Bosch 0231 167 070 or 043-905-205C, 0231 176 028
Points: 01 011
Points Replacement Plate Assy: VW 311-905-227A, Bosch 1237 110 064
Condensor: 02 054
Rotor: 04 033
Dust Cover: 039-905-241, Bosch 1230 500 139 > 1230 500 147
Cap: 03 010
Distributor Cap Clip: 034-905-265, Bosch 1231 251 033
Parts Kit (Shims, Washers & Hardware): 059-998-211, Bosch 1237 010 007
Coil: 00 015 (Blue Coil: 00 012)
Vacuum Can: 07 223 (1237 122 969) (Formerly 07 091 [1237 121 851]
Ignition Wires: 09 001
Spark Plug: W8AC
Timing Set At:: 5deg ATDC @ 800-950rpm w/strobe, vacuum hose(s) connected.
Advance/Retard Range: Vacuum: 9-12deg Adv, 11-13deg Ret; Centrifugal: 6-12deg @ 1500rpm, 22-25deg @ 3800rpm

P.S. $100
http://www.philbingroup.com/rebuilt/cat ... -0916.html

[hambone]

DVDA
VW 113-905-205AJ

Just thought I'd pass it on. I understand Colin's P.S. now.

From Samba:
DVDA stands for Dual Vacuum Dual Advance and SVDA stands for Single Vacuum Dual Advance.

Dual advance means that the distributor uses both engine vacuum and rpms to advance the timing. Those distributors do a better job of timing the ignition than mechanical advance only distributors (009 for example) because it adjusts the timing for engine load via the vacuum signal. The mechanical advance only distributors base timing only off of rpms and thus have no clue how hard the engine is being driven. You will typically see an improvement in fuel economy with a dual advance distributor (either DVDA or SVDA).

Now the difference between the dual vacuum and the single vacuum is in the vacuum advance unit. The single vacuum, as the name implies, has a single vacuum source to base the advancement of timing on. The dual vacuum unit has a second vacuum source which actually retards the timing along with a unit to advance timing with. This was done mainly for emissions reasons.

[sped372]

I have to concur with Colin's recommendation. If you can get a DVDA in proper working condition the 34pict carb combo works so much nicer. Once you have it all hooked up your idle is way back at 5ATDC so you end up opening up the bypass and the transition (taking off from a stop especially) is much smoother. Almost like, well, they designed it that way or something.

[hambone]

Very cool to know...I am in uncharted territory! Funny how often that happens...so many variables.
Thanks again guys.

[Amskeptic]

I have to concur with Colin's recommendation. If you can get a DVDA in proper working condition the 34pict carb combo works so much nicer. Once you have it all hooked up your idle is way back at 5ATDC so you end up opening up the bypass and the transition (taking off from a stop especially) is much smoother. Almost like, well, they designed it that way or something.

I am currently enjoying a 30Pict3 with vacuum-only distributor as fitted to a 1970 bus, and I love its driveability. It is just always there for you, waiting to unleash 48 mighty net horsepower to launch you to 60 miles per hour in a smooth rush of . . . . . generator noise.
Colin

[hambone]

What is the benefit for the 34 PICT? Is it a larger carb? Oh the glorious '70s, the hatching egg of our current American lifestyle.

[Amskeptic]

What is the benefit for the 34 PICT? Is it a larger carb? Oh the glorious '70s, the hatching egg of our current American lifestyle.

34Pict3 is a larger venturi carb to take advantage of those spiffy dual port heads.
Colin