Pertronix SVDA Ineffective Vacuum

[spectre6000]

I installed a new Pertronix SVDA, and it seems the vacuum advance isn't really working. I had to take it apart several times to get the mechanical advance section to not cook my engine (the stop tabs were all the way out and there was WAY too much internal advance to be good for an air cooled VW engine). I never checked the vacuum advance before rectifying the mechanical advance, so I can't say it ever worked. If I disconnect/clamp the vacuum signal line (from the vacuum signal ports on dual IDFs), I get a standard amount of mechanical advance. If I leave it hooked up I get the same amount of advance instead of the expected mechanical plus vacuum (which I think should add about 10° at max advance with no load). There is a known issue with the rubber grommet of the Pertronix unit interfering with the vacuum advance part of the distributor by either preventing it from moving or getting it stuck at some point in the advance curve for about the same reason, and I adjusted things to prevent this. If I suck on it with my mouth, I can get it to actuate, but it's like trying to suck a thick milkshake through a straw.

Is my expectation of additional advance from the vacuum section with no load inaccurate?

Is it possible the Pertronix vacuum unit is not sensitive enough for the vacuum signal it's actually seeing?

What's up?
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[Glenn]

What carb?
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

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[spectre6000]

Dual 40 IDFs.
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[[email protected]]

First, remove the cap and rotor, suck on the hose, is the distributor advancing? A common problem with that distributor is the advance mechanism hitting the grommet for the wires going through the distributor body. I have notified Pertronix time and time again but they won't fix the issue, you have to.

secondly, put a vac gauge on the hose, what reading are you getting? If I recall you are at 6k', your vacuum WILL be lower there at elevation.
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[spectre6000]

John, I did everything you suggested save the vacuum gauge (don't have one handy) and noted it above in the OP. You have a pretty good memory though, I live at 8k' for the next week and a half, and will be doing everything at about 5400' after that.

Let's say I can find a vacuum gauge at a FLAPS nearby, what should I be expecting as a reading, and at what reading should the vacuum pot actuate to what extent? I imagine rigging up a T between my mouth, the vacuum pot, and the gauge, then sucking until there is an appropriate amount of actuation.
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[udidwht]

Same here...so don't worry about it too much. Best guess is the diaphragm is stiff and the distributor internals mainly spring) are stiff as well. Combine that with your IDF's/altitude and well...you get the picture. With my set up I see 5BTDC//28full mechanical//33 with vac advance.

What cam are you using?

Who/where did you buy the Pertronix from?

Run your bus up to 3400 or so RPM's and play (feather) the throttle while there and you'll likely see ~5 or so advance. Give it some time and perhaps you'll see some additional advance.

Do you have only 2 vac lines to a 'T'? From cylinders 1 & 4? If so, you may be getting a low signal/pulses in the line. Possible fix would be the use of an anti-pulse valve.
_________________
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Bosch SVDA w/Pertronix module (7.5 initial 28 total @ 3400rpm)
Bosch W8CC plugs
Pertronix Flamethrower 40K coil
S&S 4-1 w/Walker QP 17862
3 rib 002 Trans
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[spectre6000]

It's in a Ghia. The bus that belongs to the mirror in my avatar was sold a while back. I figured stiffness would be an issue, but it's got about a thousand miles on it so far, and I would hope that it's loosened up by now... I've got timing set at 10° at idle, and I need to drive it around a bit more but if anything it needs another degree or two. It's really hard to tell when you have to gauge things over the course of 3k' elevation change between home and (anything).

Cam is unknown (as is displacement at either 1600 or 1641), but is a touch on the warmer than stock side. My guess is a 110.

Pertronix is from Appletree. A VW parts house I was previously unaware of, but after looking through their catalogue, it's all EMPI so I probably won't be ordering from them again. Regardless, a Pertronix SVDA is a Pertronix SVDA as far as I'm aware.

I have two vacuum lines teed off one and four. I've not heard of an antipulse valve or its use with IDFs, but it makes sense. Where would one obtain such a thing, and is it a good idea on a dual IDF setup?
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[udidwht]

[[email protected]]

We did send a bunch of defective Pertronix SVDA's back not long ago. It's possibly Appletree sent you one of the bad ones without knowing there was a problem with them.

To find out you have to take that cap/rotor off and check it YOURSELF.
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It's just advice, do whatever you want with it!

Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net

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[spectre6000]

What was defective about them? As stated in the OP, AND my third post in this thread, I did take the cap off and check, etc. multiple times. I was giving serious thought to buying a Bosch vacuum unit and replacing the rest of the guts with the guts from a Bosch 009 in an effort to recreate the venerable ACN SVDA that I enjoyed so thoroughly on my bus (had I know they were going to be discontinued so soon I would have put a 009 on it before it left).
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[spectre6000]

What's up with only being able to find the anti pulse valves in the UK?
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[E4ODnut]

I'm not trying to be nasty or anything here, but you seem to be in a big hurry to blame the distributor. You may indeed have a problem with the distributor, but how can you determine that without knowing what the vacuum signal is that you are sending to it under all speeds and loads, and what the advance curve of the vacuum pot is?
I would suggest that if you determine both of these things you will find the answer to your problem.

[udidwht]

[GTman]

Jason

Check out some of my earlier posts in the forum on virtually the same issue.

Not only is my Pertronix SVDA insensitive to anything less than an 8 inHg vacuum signal which is difficult for any dual carb set up to realize but I too had to shave down the rubber grommet to get the advance mechanism set up to work properly.

Even after this at 3000 rpms and 30 degrees timing my idle timing is 15 degrees so I'm only getting 15 degrees of mechanical advance which is inadequate.

The distributor is junk. I live by Pertronix here in Los Angeles so will be taking it in this week for their tech people to troubleshoot.

Ill keep everyone informed. Good luck.

Thanks. Grant.

[udidwht]

[GTman]

I did speak with one of the technical people at Pertronix this week and that told me that their vacuum canister needed at least 8 inHg and provided full vacuum advance at 10 inHg. I have verified this by removing the vacuum canister and sucking on a teed off tubing connected to it and a vacuum guage. You start to get some slight movement at 6in Hg, but this is removed from the distributor so my thought is you need the extra 2in Hg to get the vacuum canister arm to move the breaker plate when installed as the breaker plate does have some friction and is held in place by a lubricated ball.

Regarding the vacuum mechanism I saw that when at rest it was hitting on the rubber grommet, so was not allowed to fully retreat to zero. When I shaved away some of the grommet my timing at idle was about 5 degrees retarded.

But now I have an issue with the mechanical advance itself as I'm only able to get 15 degrees of curved advance from it. I will remove the distributor this weekend and investigate. But at this point I just want to put this baby in Pertronix's hands and let them explain to me the workings of their distributor.

I have heard of others replacing the Pertronix vacuum canister and replacing it with a more sensitive one, e.g., one responsive to vacuum signals of the 3 inHg or so that dual carb ported vacuum is easy to hit. I would love to hear more about this option.

Thanks, Grant

[spectre6000]

I just got back from the flats and picked up a vacuum tester at NAPA. I have crap going on all day tomorrow, so I'll be checking to see what I'm dealing with sometime this next week.

GTman, out of the box I had something like 30 degrees mechanical advance. I had to tear it apart 3 or 4 times to get the stops to where I had an appropriate amount.

E4ODnut, given the reputation of this particular Pertronix distributor, my experiences with the distributor thus far, the insane amount of work I've put into this car over the past few months (everything has been replaced or rebuilt save the bottom end of the engine, the tranny, and the paint and body) I don't think it's even remotely far fetched to suspect that (as GTman found out for us) the vacuum signal required to actuate the vacuum pot is higher than should really be expected from a dual carbed VW (especially at this altitude).

Luckily, these distributors, aside from the quality of specific components and the lack of tune/testing out of the box, are pretty good copies of the Bosch units and the parts seem to interchange pretty easily. Once I narrow things down to verify the signal requirements of my specific vacuum pot and what it's seeing, I'll either do what I can to rectify things or see if I can dig up a lighter Bosch unit.
_________________
Jason Hopper

-'58 German Market Deluxe Beetle (in progress)
-'84 M1009 CUCV
-'81 K10
"Buy the best, cry once." -Gene Berg
"A cheap man will always buy the cheapest thing available, and then buys another one hoping for a better result, and then spends the rest of his life in misery complaining about it. A thrifty man will buy a good part once and never think about it again." -RockCrusher
"Don't feed the Shitty Parts Monster!" -Me

[GTman]

Jason:

If you decide to change out the Pertronix vacuum canister to a Bosch unit that is more sensitive to the ported vacuum of a dual carb set up (say 4 to 6 inHg) please let me know.

I am battling a flat spot with the dual Kadrons that I am running on my 1600 and want to make sure that I've eliminated timing as an issue (before I start messing the accelerator pump adjustments).

If I learn anything from the Pertronix tech about possible alternative vacuum canisters that they carry I will let you know.

Also, when you were adjusting your centrifugal or mechanical advance, what was is that you needed to do. Sounds like you had too much initially.

Thanks, Grant

[modok]

The little handheld vac pump with a gauge on it was a very useful tool back when cars had a lot of vaccum stuff, not so much anymore now that everything is electric. I don't even have one anymore, but that's what yall need to calibrate these distributors and stuff.

Alfa needed a one way valve in line to generate enough vaccum to run the distributor, I wonder why VW doesen't??? hmmm, well you can make one easy enough if needed.

[spectre6000]