TheSamba.com :: View topic - Almost ditched the Kadrons yesterday, learned a lot, now SVDA?

Wed Jun 15, 2016 9:21 am

Well after 3 days of putzing around with these carbs, ignition, timing and such, I finally found the problem. It's a stock 1600 DP in our dune buggy, which isn't on the road yet, but are working to get it ready for July. We bought it a few months ago and it came with 2 engines, one with a Holley progressive 2 BBL (Weber copy) and the other with dual Kadrons and Pertronix 009 distributor. Got the single 2 barrel going first and had it running pretty well, then I noticed that there was no manifold heat pipes connected under the huge PIS center mounted plenum. Crap! We live in a cool part of the country and I didn't want to be fighting icing so out with that engine, and in went the dual Kadron engine. Got that running right away, but it was farting and barking out the exhaust and just couldn't get it right. I had another set of Kadrons that looked much better so swapped in those. They had all the correct jets as well. Spent 3 plus days reading articles on the web about tuning these, what distributor to use and such...still couldn't make them acceptable. Two sets of carbs both running like crap. WTF. I finally found a video (Jeff I think) on what to look for in used Kadrons...well crap. I checked all carbs again and although all the jets were the correct markings, 130 mains, 150-2 air correction and 55 idle, upon close examination the bloody 130 had been soldered and re-drilled in one set of carbs, the air correction jet was way bigger than a 1/16" drill bit, in the others...JEEZZZZ :roll:, I think the 55 was was the only unmolested jet. Quick trip into town to my favorite VW place and home I came with a selection of jets. 127.5, 130 and 137.5, the only ones he had. Also picked up 45 and 60 air jets. I put in 130 mains, 55 idle and used the body that had original air correction jets, un-drilled. Oh, I also had to drill and install the vacuum port on the good bodies, everything went together nicely.

Okay, now we're talking. Got it running really nicely last night, (still just in the driveway, body is not on yet) but the popping is gone, she purrs like a kitten at idle and revs nicely with no stumble or hesitation. :D

HOWEVER, all of this is with the distributor I put in, a vacuum advance unit, but connected to MANIFOLD vacuum, not ported from the carb. I ultimately will have an SVDA installed and will be rebuilding one today, but the one in there has the same spec vacuum can 180mm HG, 8-12*. The carbs both have the vacuum port added, and confirmed that the mod was done correctly, bottom hole plugged etc. I can see the vacuum signal when I blip the throttle, get about 10-12 inches vacuum, holds at about 5-6" at 2000 rpm, but it is not enough to get the vacuum can moving at all. I tee'd the balance hose going from side to side on the manifolds and ran a line to the vacuum canister and BAM, full 10* advance at idle, so I know the can works and the plate moves. I have about 18" manifold vacuum at idle. I tried both carbs singly, then tee'd together, no difference. I know vacuum doesn't add, the signal just gets smoother from the carb ports when tee'd.

So I have a few questions.

1. Anyone who has their Kadrons running correctly with vacuum advance, I would like to know your vacuum readings going to the vacuum can when you blip the throttle, and can you see the timing jump on the crank pulley?

2. Why can't we use manifold vacuum on these engines with dual carbs? The most common comment I see "won't have a stable idle". Mmm, I can back my idle back down to just barely turning over and she will sit there all day long, just purring. At 1000rpm it's also very stable. Would really appreciate someone who KNOWS these carbs and SVDA type distributors to step up and explain why we shouldn't use manifold vacuum, or.....let me know how to get a decent signal from the carb ports. :lol:

Wow! That was a long post. I have read so many similar posts over the last 10 years or so, and have really not been able to find a good answer. Hopefully others going down this road in the future will be able to benefit from this thread if we find a solution.

Thanks all!

Cheers

Oh, to add. Set the valves to .004" and .006" cold, timing static at about 10, full advance at about 30 without vacuum.

Wed Jun 15, 2016 9:45 am

Manifold vacuum is incorrect for these carbs, as you would be pulling the most vacuum at idle, and only advancing the can while at idle. As soon as you hit the throttle the vacuum would drop off.

The port in the body of the carb is just above the edge off the throttle plate, that way once you begin to open the throttle it uncovers the port, which allows the vacuum to pull the advance in immediately to prevent the stumble associated with 009 or 050 style distributor installations. You can often bump up to as bigger idle jet, and adjust for more accelerator pump squirt to make them work better though.

There are two drilling in the carb that lead to the same port on the side, if whoever modified the carb(s) for vacuum didn't block off the bottom port in the carb you would not get the proper vacuum signal

I don't have measurements for you, but my SVDA advances just fine with the kadrons I modified myself for vacuum. Without the vacuum line attached you can see the advance doesn't move right away when observing with a timing light. Hook up the line and the advance moves immediately and quickly. I have both carbs set up and hooked together with a tee...

Do you have pictures of how yours are set up?

Wed Jun 15, 2016 9:49 am

http://www.thesamba.com/vw/forum/viewtopic.php?p=8115579#8115579

There's a walk through on how I modified mine a bit down this page showing a bit of info.

Wed Jun 15, 2016 10:03 am

Thanks for the quick reply and thoughts. Yes I did the vacuum port mod myself and confirmed I epoxied the bottom hole correctly by spraying carb cleaner thru the port from the outside and watching it exit only from the top hole, above the plate.

Now, my thoughts are, and I am really hoping this can be corroborated, when at idle, yes, the way I have it now the canister has full vacuum, and timing is sitting at 20* at idle. In the ported world, timing is sitting at 10* or whatever static is at, and when you crack the throttle, the canister sees a portion of the manifold vacuum and as the throttle is opened wider sees more of the manifold vacuum. So wouldn't the manifold vacuum connection have similar if not the same vacuum at say half throttle? Or am I missing something in my carb theory and there is actually a stronger vacuum signal in the carb port caused by air flow thru the venturi? This is where I could really use some help. My carb ports just don't have enough vacuum to get the can moving when I blip the throttle but connected to manifold vacuum I can see the timing sitting at 20* and it slowly climbs to 30+ at 3000 RPM. Of course this is no load on the engine and may be completely different under load, but I should still be able to see the timing jump with ported vacuum, just sitting in the driveway.

Cheers

Wed Jun 15, 2016 11:22 am

You are only seeing the advance climb when blipping the throttle because the centrifugal advance is coming up and taking over as the manifold vacuum is going down.

The way that the advance works is similar to the venturi effect, as the airflow increases through the area between the wall of the throttle body and the throttle plate it pulls vacuum through the port. As the throttle plate is opened more the vacuum pulling through the advance port (which is right at the edge of the throttle plate) decreases, and it decreases at a different rate than the amount that direct manifold vacuum would. This is the difference between ported vacuum and manifold vacuum. As the vacuum through the advance port decreases the centrifugal advance in the distributor has already taken over partially, and you will see a reduced vac signal. This is how the vacuum advance works off-idle and is not pulling at idle.

You should have around 5~12° advance static at idle, and around 28~32° total, and connecting the vacuum advance canister should not increase the advance until the throttle is opened, If it does your throttle plate is open too far. Manifold vacuum is not used on any of the VW distributor setups for advance, they all only use it for either vacuum retard or for additional emissions or autostick uses.

Wed Jun 15, 2016 2:28 pm

I used to be all about ported vacuum until I realized ported was developed for smog reasons. Pre smog vehicles with vacuum advance ignition used manifold vacuum.

If you are using an original Bosch vacuum advance you can get away with using ported vacuum as kadrons only make around 4-5 inches and the light springs in the stock distributors will respond. Aftermarket reproduction vacuum canisters have heavier springs that require at least 8 inches to work properly and even if you use a T and antipulse valve you wont get it to work right.

The last few setups Ive played with I use manifold vacuum and adjust the mechanical advance in the distributor to get to where I want the timing to be. Ive found 10-12* idle and 36* total works best for around 8:1 compression/mild cam, tall deck builds. Lighter vehicles, low compression or hemi head will benefit up to 40* total.

First I plot what the mechanical vacuum advance is then see what the additional vacuum gives then modify the advance stops to get more or less total advance if needed. I try to get it as close to factory spec as possible

I use a 1/2 crossover tube and tap that for the canister vacuum. A cylinder head temp gauge is mandatory to help tune and ensure you dont melt your heads especially if its hard to hear the knock over carb/valve train/wind noise. Monitor plugs for lean conditions or signs of detonation as well.

Most will disagree but you have already seen the benefit of MAP and just need to dial it in to your specific build. If you ever upgrade your ignition (Black Box, etc) you will notice that it uses manifold NOT ported vacuum as the signal to the computer. By manually modifying the distributor curves you are doing the same thing the timing map would do.

Good luck and keep on tuning!!

Wed Jun 15, 2016 2:46 pm

Cool. How do you keep it from advancing too much at idle? Ever since I sold my Sun dizzy tester I've been jonesing for another way to set curves easier, so most of what I do is from past experience and testing.

MAP is great for ignition and EFI tuning, for sure. But for distributors that expect ported vacuum I don't see how you could easily set them up to run off of MAP or manifold vacuum....

Wed Jun 15, 2016 3:21 pm

with the stiff canister springs in the chinese svda (petronix, hot spark, etc) the additional manifold vacuum at idle barely affected timing so I was able to just rotate the distributor to get where I wanted it. The main problem with the aftermarket stuff was the total MECHANICAL advance. The last 3 petronix units Ive worked with had 40* mechanical instead of the correct 25*. If you check timing like most and set it with hose off and plugged and then just reconnect without checking total it could be 50+*!!

When using original used Bosch I would use various springs until I got what worked best, but since good used, affordable cores are gone Im now using electronic programmable for all future projects. Its now the best time and cost effective way to get the appropriate curve for application.

Canisters dont care if they get ported or manifold vacuum especially aftermarket junk, what Ive found is most important is to actually plot what it is doing with your engine combo and tune to works best for it. All manuals give parameters for factory stock builds, since we modify far from factory its important to listen to your specific engine to see what works best.

Its just like carb jetting, you can get a baseline on general combos but combustion efficiency plays a more important role on what really works best. The amount of variables is staggering and for someone to say this is what you need is just generalizing. It will run but wont get the best MPG, power or drivability.

Wed Jun 15, 2016 9:10 pm

Lingwendil wrote: You are only seeing the advance climb when blipping the throttle because the centrifugal advance is coming up and taking over as the manifold vacuum is going down.

That's the problem, I am NOT seeing the advance blip, what I am seeing is the vacuum gauge blip, the timing stays at 10* until the RPM climbs then the mechanical starts to work...giving me about 30* at 3000RPM. As mentioned, the canister needs more vacuum than the Kadrons can supply, hence my connection to MAP. I have a half dozen decent original Bosch distributors, mostly complete and/or already working, I just need to figure out the curves.

AlteWagen, nice job on the graphs, and thanks for the help. I started looking for a Sun machine locally but they seem to have all been recycled. :cry:

I'll be up bright an early tomorrow and have a good look at what I have and post some #'s. I will probably restore the 034 and play with various canisters to see if I can ported vacuum to work, otherwise, I start playing with springs and such.

Thanks all!

Cheers

Wed Jun 15, 2016 11:09 pm

Okay, after entering all the data in Excel, I had to figure out how to get it into an image, and then here...an hour later... :roll:

These are the distributors I have to play with. Hopefully the chart makes sense. The right most column is degrees advance @ mm Hg, didn't feel like translating to inches. However 25.4mm = 1"

Thu Jun 16, 2016 12:11 am

Your best bet is the BR8. Adjustable limit (rod) and diaphragm spring too. Non resister rotor is available and a bonus. Bremi replacement parts are better quality than bosch too.

Thu Jun 16, 2016 4:51 am

This is very good stuff....Going to go back through after another cup of coffee... Thanks for all the data.

Thu Jun 16, 2016 8:33 am

Data? You want data? Looky here...

EverettB posted this last year...amazing

Curves
http://www.thesamba.com/vw/forum/viewtopic.php?t=617242

...and Andy posted this chart which has most 60's-70's distributors and parts.
Bosch Chart
http://www.thesamba.com/vw/archives/manuals/bosch_tune_up_parts.php

Many hours of good reading...and very useful data.

Cheers

Thu Jun 16, 2016 8:36 am

AlteWagen wrote: Your best bet is the BR8. Adjustable limit (rod) and diaphragm spring too. Non resister rotor is available and a bonus.

I agree as well.

Fri Jun 17, 2016 7:40 am

Well I spent the entire day working on the buggy yesterday, most of it on the ignition system.

I started out with the VJU4 BR8 and got it all apart and cleaned and back together then I couldn't get the screw adjustment to turn inside the nose of the vacuum canister, on either if them...so I put them aside and went onto the 034. Got it all rebuilt and looking nice, even put a high buff on the housing, I hear that helps keep it in tune. :roll: All cleaned and greased with MagnaLube, similar to Superlube, a teflon based grease in a tube. Tested the vacuum canister and I ended up using a 505 instead of the original 579 as the 579s' nipple was broken off. The 505 just need a little less vacuum to pull in. One thing I discovered and was very disappointed...you can't put in a Pertronix Igniter module in a vacuum advance distributor. :( At least I couldn't see how it would work. So I used a good set of points and condenser.

Fired it up and everything sounded good. What a difference having free weights makes. Vacuum disconnected I can now see a nice gradual climb from 10* static up to 20* at 2,000RPM, then slowly rise to 32* at 3,500RPM. Nice!! :D Connected the vacuum to the Kadrons T connection and nothing, nada, zipp, zilch, no advance at all. Buggar! Okay, I'll keep MAP and hope it works when I get it on the road. It runs great in the driveway and is smooth and picks up perfectly. It idles at 20* and then climbs slowly to 32* or so, and gets a little higher depending on how I jazz the throttle.

So at the end of the day, I was sitting on the deck having a beer and thinking about the Kadron vacuum problem and I thought I should try just one carb, instead of both tee'd, maybe the T is causing a cancellation of signals. Tried just the left carb to the can and voila! I have ported vacuum advance! :D :D
I think when the 2 carbs' vacuum ports are tee'd, the pulses are out of phase and as a result, cancel each other, or at least reduce the amplitude of the signal. I confirmed this on the vacuum gauge, with both connected the signal is smooth, but low, with no big jump, maybe max of 5" Hg. Just one carb, peaks of 12-15" and steady above 6" Hg at 2000RPM. I can see the timing jump up to 40* at some throttle blips and only 30 without the ported vacuum so I know it's working, and not the mechanical advance.

Cool! Having a beer does help with mechanical problems. \:D/ :idea: :D

I will play with the other distributors later, for now, I need to focus on getting the buggy on the road...fine tuning will come later. Just glad I was able to get the carbs and ignition working happily together.

Here it is...

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Fri Jun 17, 2016 8:23 am

Nice!

Having it ported will work out better for sure. glad to see you got it figured out 8)

Now you can try swapping springs around to play with the curves if you're into that sort of chicanery :lol:

Back when i had my curve tester i found a spring from one of the old empi distributors turned one of my SVDA's mechanical curve to a pretty damn close analog of an 019. with vacuum hooked up that was the nicest dizzy I've ever run on a daily driver with a stock 34PICT3. Sure wish i hadn't of left it in the car when i sold the car, I don't have the same stash of parts that I used to, but it would have been neat to try it with these Kads.

Fri Jun 17, 2016 8:40 am

Lingwendil wrote: Nice Now you can try swapping springs around to play with the curves if you're into that sort of chicanery :lol:

Oh yes, I will, but now will wait until it is on the road, see how she does as is. I started looking around for an old Sun machine but seems they are all gone in my area. Still may find one....would be fun to play with. Have a few cars that I could tune, several MGBs and a '68 Firebird ragtop, plus all of these dune buggies. :roll:

Cheers

Fri Jun 17, 2016 10:48 am

ve7kilohertz wrote: I started looking around for an old Sun machine but seems they are all gone in my area. Still may find one....would be fun to play with.
There was a Chevy dealer that shut down a couple of years ago here in town. They had an on-line auction for most all of their shop equipment. I kept bidding on their big Sun engine analyzer and their Sun distributor machine. They were ancient, a lot like the ones we had in auto shop class in the mid 1970's. I figured that as big as they were and since we're kind of out in the sticks, maybe nobody would want to pay a lot and then drive all the way out here to get them. Somebody wanted them both worse than I did. :cry: They kept outbidding me, but they still went pretty cheap. I really wanted that distributor machine too. :roll: Got a few tools at really good prices though. Felt a bit guilty at how little I paid. 8)