Pertronix SVDA Ineffective Vacuum

[Todd66]

My setup almost doubled the reading on vacuum gauge, and smoothed it out completely. I am sure the anti pulse valve would be the same. If you installed a carb jet in line (between carb and dist) I can see how it would help, not sure if it would be as effective as valve. If one was to do this, I would think installing it closest to carbs would be the most effective. That way the vacuum line between jet and dist would act as a dampening chamber and reservoir for vacuum.

[AlteWagen]

I just finished rebuilding a SVA 205N and the tip of the nipple on the can has an insert that is the size of a small jet. The can on a 205T has the same size opening as a stock 034.
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Official Dual Carb Thread
Cylinder Head Quick Reference Sheet

[blacktruck]

ballpark size of that opening please?
sewing pin,toothpick maybe?

[AlteWagen]

Just stuck a 65 jet gauge in there

edit: added pic
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Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet

[blacktruck]

thanks
welding tip by "seat of the pants"was OK
back to the dungeon/partspile

[spectre6000]

Your setup (essentially being a makeshift antipulse valve) doubled and smoothed the vacuum signal? I just want to be clear before I go drop money on something. This would be the closest anyone has come to having an answer to that question in the two months or so since it's been raised...
_________________
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]

A good indicator of engine load is what is required to adjust timing for load, as opposed to strictly engine RPM. Manifold Absolute Pressure, or manifold vacuum (same thing, different points of reference) is a very good indicator of engine load for most relatively stock engines. High lift long duration camshafts as well as multiple venturis will increase low and mid range load MAP (decrease manifold vacuum), which makes it harder to indicate actual load. That's not to say it can't be done, it's just harder. If you are using a conventional vacuum pot advance mechanism, then you will have to use one that operates with less available vacuum, or better still, has some range of adjustment. These vacuum pots seem to be quite rare.

As far as the vacuum signal itself is concerned, every cylinder will create a vacuum signal. If you just tap into one intake runner the signal will be very jumpy just because the runner is only under vacuum for approximately 1/4 of the engine cycle. If you have a multi cylinder engine you can get a pretty good average by using a small plenum manifold and plumbing a signal into it from each cylinder. This has the effect of raising the average signal over the complete cycle and smoothing it out. Even with this it is often desirable to smooth it out even more. Typically a restrictive orifice is placed in the line to the vacuum gauge, pot or MAP sensor to dampen the signal. It does not amplify it, it just smooth's out the bumps, so to speak. Typically this orifice is ~ 0.030" but whatever works best is usually found by experimentation. Go too large and it's still jumpy, go to small and you loose amplitude and response time.

Vacuum pots are pretty crude critters, but they work very well when mated to an engine they are designed for. If you have a modified engine then your choices are limited. From my point of view the only practical option is to go electronic. For one, CB's "Black Box" should be the ticket if it works as advertised.

[74 Thing]

http://www.thesamba.com/vw/forum/viewtopic.php?p=3141983

Here is one of the earlier posts about the welding tips or idle jets to act as an anti pulse valve.

[[email protected]]

[marbleknight]

Hi folks, just thought I would throw this in: I've been wanting one of these distributors for a while, and I too had an Amazon card. I got one the other day. Package arrived today and I immediately did a vacuum test on it after doing a visual inspection to see if the rubber wire grommet was interfering with the vacuum advance. There seems to be no interference there, well maybe just a smidge but certainly not enough to impact the function of the device. Anyone who's read my posts know I'm pic-mad so here are a few and then I'll show you the video of the vacuum test.

So that's the thing out of the box. Looks really sharp. After the visual inspection I hooked up a vacuum gauge to see where the advance starts to kick in and where it reaches max.


Link


So it looks to me like the advance just starts to move at between 3 and 4 inHg. It reaches full advance at about 9 inHg. Based on the vacuum readings I get from my carbs, I think that's pretty reasonable. I'll try to post a vid a little later on of how much the carb is pulling at mid to high RPM. The vacuum line is only attached to one so I may have to get the other one in on the action... Anyway, hope this helps. My 2 cents is y'all got a bad lot.
_________________
1974 Bug - 1791 (85.5 x 78mm) "Stock Stroker"
1974 Bug - 2021 (92TW x 76mm)

[SBD]

I've had a new one of these distributors just sitting in the box waiting on my stroker build. I already took care of the grommet interference. Now that my new vacuum/pressure test gauge has arrived I'm going to have to dig out the distributor & check the advance.

[TKentT]

[spectre6000]

[marbleknight]

I understand the idea of having a spec, but it doesn't mean a whole lot. Wouldn't you agree that each type of carb is going to pull a different vacuum at the same RPM? What if my carbs pull a much lighter vacuum overall? I'd rather have an "out of spec" advance that starts to kick in at 2000RPM or even less vs twice that much or not at all because the freaking pot is stiff and doesn't work worth a dam... Come to think of it I'd like to see other people do this same test to see if there really is a tenable 'spec' or if it's just something Pertronix pulled out of thin air. It took 5 minutes to set the test up and less than that to suck on a tube.

What matters in the end is 1. What vacuum the carb(s) pull over a given RPM range, and 2. How that matches up with pot mechanics, i.e. how much the advance moves at a given vacuum level. Having thought about it for a bit I think one must measure the ported vacuum level at various RPMs, document that curve, then measure the movement of the vacuum advance at various vacuum levels and document that curve. Then see how well those two curves coincide with one another. If they don't play nice with one another, you have work to do if you really want to tune the engine.
_________________
1974 Bug - 1791 (85.5 x 78mm) "Stock Stroker"
1974 Bug - 2021 (92TW x 76mm)

[spectre6000]

The spec is what Pertronix's supplier is supposed to be manufacturing parts to. If they don't meet these specs, each distributor will be wildly different (which pretty much seems to be the case), and it's not possible to produce predictable results with the part. That nit picking aside, you're right. What matters is the specific application, and if you get lucky and get a vacuum canister that is way out of spec on the low side and you're running a dual carb setup, you've won the Pertronix distributor lottery.

Otherwise, I'm hanging up the the towel on this endeavor. The most recent response from Pertronix was (and I'm paraphrasing only slightly), "Let me know how the anti-pulse valve works for you." This demonstrates to me that they're really not all that interested in making the product better. Combined with the fairly extreme deterioration in performance of my own unit over a very short period of time with very few miles (stiffening rather than loosening of the already too stiff vacuum canister and the dramatic increase in slop in the vacuum advance plate), I'm putting these distributors in the junk category. Buyer beware.
_________________
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

[AlteWagen]

So what will you be using on the DD? Black box looks better everyday.
_________________
Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet

[spectre6000]

I'm just going to run it for now. It's essentially a shitty 009 as is, and they technically work. If it becomes an issue (and/or I can find the time), I'm pretty sure I have a zillion cores of varying sorts that I can cobble something together with. I work from home, so my commute is about 15 feet in my PJs. I drive it to the grocery store, meetings across town, errands, and nice drives in the mountains when the roads are nice.
_________________
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]

Update:

Sorry for the wait...first bus day in awhile given I try to avoid driving her on less than what we have weather wise today here in Seattle area.

Anyhow...I threw my timing light on the bus after a good warm up and the timing check since my last when I put on the anti pulse valve appears to have changed slightly. After the install (2-3 months ago) of the valve a few hundred miles ago I set the timing at 28 full hose off plugged) and it would idle at 5. With the hose on it would show ~ 32-33 degrees (vac advance) at 3300-3400rpm's.

Today however the timing shows 6 at idle and 30 degrees full (hose off and plugged) . Only change since my prior check is the miles I've put on the bus. I'm also not seeing any vacuum advance. I confirmed the distributor is snug (not loose). Idles at ~ 900rpm's.

I reset the timing to 4 initial 28 full (hose off & plugged) and still do not see any vacuum advance. I even went as far as to remove the anti pulse from the line and the results are the same.

I'm now going to recheck and make sure that nothing is jamming up the vac can arm in the distributor...but I don't expect that to be an issue given I confirmed that it wasn't when I installed the distributor initially.

Stand by...
_________________
1972 Westy Hardtop/Type-4 2056cc
96mm Biral AA P/C's~7.8:1CR
Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
71mm Stroke
73 Web Cam w/Web solids
Dual 40mm IDF Webers - LM-2 - 47.5 idles/125 mains/190 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
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
185R14 Hankook tires

[udidwht]

Well I confirmed that the vac can armature is not jamming/hitting anything. I also hooked up a vacuum gauge to the Pertronix SVDA and the results are similar to what (Marbleknight) showed. Mine would start to move at 4inHg and top out at 10inHg...the plot thickens.

So at this point I'm leaning at the combined effect of the individual throats on the IDF with the performance cam (Web 73) makes for a quirky less than stellar signal. Enough so that one is likely to see little if any vacuum advance.

This is with the bus parked with little to no load on the engine. I have both carb vac ports T'd and then onto the distributor.

It does however at this point work and feels better than my 25+ year old German 009 that I plan on refurbishing the best i can and keep as a back up.
_________________
1972 Westy Hardtop/Type-4 2056cc
96mm Biral AA P/C's~7.8:1CR
Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
71mm Stroke
73 Web Cam w/Web solids
Dual 40mm IDF Webers - LM-2 - 47.5 idles/125 mains/190 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
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
185R14 Hankook tires

[57baja]