Issues with Type1 Dual Port - Idle

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hambone
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Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 07, 2015 11:06 am

Hello, I'm trying to get Bus2 to idle correctly. She is timed correctly, correct fuel pressure, dwell ok. I am running a 34 pict with a dual vacuum distributor. Basically it idles and runs wonderfully but wants to conk out after the transition from high RPMS to idle, then recovers after a few seconds. I am thinking the retard on the distributor is the culprit. I am very surprised to see how differently these '70s carbs are set up, they are trying to mimic fuel injection apparently. I'm not nuts about the tubes and gizmos.

Asiab3 and I were trading PMS back and forth, but they are useful so here they are: (I don't want the damned dashpot if I can avoid it)

Bob wrote:
"Drove it around the neighborhood (they must think I'm nuts) again, perky and doesn't die at stop signs. BUT after running at high RPMS, during the the transition to idle, the RPMS drop to about 850 and then slowly recover to 1100. When the engine is cold it just dies"
Asiab3 replies:
How are you denoting lean or rich idle mixture? I have witnessed, with a half-assed explanation, that a rich idle mixture will cause a stumble and/or reduction in idle speeds under certain driving operations like:
- Shifting into N from 3rd as if you're suddenly stopped by a yellow light on a main city street, then applying the brakes from a high RPM (but in N.)
- Applying the brakes downhill in neutral while the RPMs decrease
Do you have a throttle positioner or dashpot? I should have sent one damn; I have like 7 spares. Do you have the bracket on your throttle arm for one?
Image
The dashpot slows the throttle arm closing, and does a whole bunch of emissions stuff. Since the distributor was retarded for emissions originally, the dashpot actually works in concert with the odd slow-down you're experiencing. When the throttle plate snaps shut, the engine is still sucking air+fuel. The vacuum (negative) pressure sucks WAY harder when the throttle is instantly closed but the engine is still sucking hard due to RPM. This means the engine sucks a plethora of fuel that it doesn't need for the first few seconds after throttle shutting. Add a significant retard of timing, and the fuel that gets sucked in with the extra vacuum just can't burn effectively. Enter the dashpot. It slows the final closing of the throttle arm, even when the pedal snaps back up under your foot. This eases the transition of vacuum, and prevents a significant amount of extra fuel from richening your mixture (and killing the earth, dude.)
Some '71 California cars even had the dashpot AND throttle positioner to REALLY save the planet:
http://greencascadia.blogspot.com
http://pdxvolksfolks.blogspot.com
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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 07, 2015 11:36 am

P.S. the only deviation from stock is the pilot jet, which was turned out and glued in place due to idle issues.

lookit
http://www.thesamba.com/vw/forum/viewto ... 17&start=0
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http://pdxvolksfolks.blogspot.com
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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 07, 2015 1:36 pm

It's better, think it was the fast idle screw, it was way the hell in causing the other settings to be way off. It is now 1/2 turn past contact with the choke cam. The idle air screw is also way the hell out now but it seems to work.
The engine seems to be happiest at slightly rich at idle, is that ok? If I lean it further the engine dies or runs hot.
Time will tell, but I can't get it to die yet. Time for another test drive.
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http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 07, 2015 3:24 pm

It still wanted to conk out after a run. Had to screw with the mixture a little more, it sure likes it rich. Also screwed in the fast idle screw another 1/4 turn. No more dying after high RPM for now, but it seems to change day by day! I did drive all over the neighborhood it seems to like it. Also running slightly hotter than I'd like but it seems to be a new engine, maybe some high performance crap. An unknown Strictly Foreign engine from Grants Pass. Runs well but of course the PP is out of balance...
I wish I could deal with this "slightly rich" thing. Get a slight puff of dark smoke on the first revvvv after idle. I've seen a few engines where I can't get rid of that symptom, it bugs me. Is it a jetting thing, or because I messed with the pilot jet? It is glued I don't want to have to move it unless I have to. All and all it really runs great, much peppier than my single port Bus1. Couldn't keep up on the way to Hambone.
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http://pdxvolksfolks.blogspot.com
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asiab3
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Fri Aug 07, 2015 5:13 pm

Ok so you don't want the dashpot, but why? It's job is to prevent this symptom by eliminating the cause. And it does nothing else... ;) Your changing of the fast idle screw is doing exactly what it does, but the dashpot does it dynamically and then lets off so you still get max air bypass through the idle circuit.

Speaking of which, you have a hole in the throttle butterfly, right?

The idle air bypass screw SHOULD be farther out than you're used to, because the timing it more retarded at idle than you're used to.

My first test would be to see if you can get this "dip" in RPM to happen in the driveway with a dynamic timing light attached.

One of these days I'll just make a trip up there and teach that paperweight some proper road manners. Your bus deserves better.

RobbieNotBobbedYet
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 07, 2015 7:05 pm

Last time I checked the dip in RPMs didn't happen. Yeah I hooked up a tach. How can a bus run both rich and great? It doesn't make sense to me.
I don't have a bracket for the dashpot, but besides that It is frustrating that a stock '69 Bus didn't need any of this stuff, it seems like adding more and more gadgets (that could go wrong) onto a simple design like the Borg. But they were chasing their tails with EPA regulations. I don't even have a charcoal canister on this bus!
It has always been difficult making the transition to 1970s engineering. It seems to lack a basic quality that made VW famous.
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http://pdxvolksfolks.blogspot.com
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asiab3
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Fri Aug 07, 2015 9:39 pm

hambone wrote:I don't have a bracket for the dashpot, but besides that It is frustrating that a stock '69 Bus didn't need any of this stuff, it seems like adding more and more gadgets (that could go wrong) onto a simple design like the Borg. But they were chasing their tails with EPA regulations…It has always been difficult making the transition to 1970s engineering. It seems to lack a basic quality that made VW famous.
The engineers were dancing on pins and needles trying to balance the legendary smoothness, reliability, and economy with a package that would pass the tailpipe-sniffing hounds. Every year got more restrictive from about '68 and onward. The drivability reward of the retarded idle only comes with the bypass-style carburetor(s) from the early '70s; if the carb isn't one that was built for the retard, it will always struggle. The drop in timing combined with the richness from throttle shutting isn't a winning combination, but those are both necessary actions, so we have the dashpot to even out the drivability.

A rich-running can run nicely, especially off the choke. But the richness of a throttle shutting on decel might just be too much for your setup.

Tell us more about the throttle plate… Hole in it?

Why the pilot jet screw out? Have another jet the same size to try and see if the jet or the carb is at fault?

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sat Aug 08, 2015 12:02 pm

I am running a "new" 34PICT-3 Mexican Bocar. When was the last time you could get a Mexican one? I've only seen Brazil. Came with the engine, also low mileage. It could be the culprit but I don't want to just throw money at the thing. I'd imagine it has the throttle plate hole but I haven't looked. Are these aftermarket carbs retard-ready? I'd imagine so if they have the vacuum ports.
Had to loosen the pilot jet because it wouldn't idle, that old fix.
Maybe I should try to disable the retard and see if that helps? But it was also running rich with the 009.
Around town it really runs great. Otherwise it's driving me nuts.
http://greencascadia.blogspot.com
http://pdxvolksfolks.blogspot.com
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asiab3
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Sat Aug 08, 2015 2:03 pm

hambone wrote:I am running a "new" 34PICT-3 Mexican Bocar. When was the last time you could get a Mexican one? I've only seen Brazil. Came with the engine, also low mileage. It could be the culprit but I don't want to just throw money at the thing. I'd imagine it has the throttle plate hole but I haven't looked. Are these aftermarket carbs retard-ready? I'd imagine so if they have the vacuum ports.
I wouldn't say "having" the ports makes them qualified. The H30/31 "has" the ports too, but the vacuum signal is completely wrong. I don't think the Mexi-bugs ever came witha retard, because they, ( in the US, at least,) came with catalytic converters to solve the hydrocarbon problem.

Look down the carb throat with the air cleaner off and choke plate vertical too see if there's a hole for air to bypass the bypass circuit at idle. (Confused yet? :D ) We're looking for the red arrow:

Image
Had to loosen the pilot jet because it wouldn't idle, that old fix.
Maybe I should try to disable the retard and see if that helps? But it was also running rich with the 009.
Around town it really runs great. Otherwise it's driving me nuts.
Disabling the retard will require a complete retune of the carb, though if you mark your positions by counting screw rotations, it should be easy enough to go back. The hole in the throttle plate is sometimes sealed up on carbs when the retard isn't hooked up, but it all depends on what your engine wants.

Remind us what your timing is, and how it's set. If you're shooting for 28-30 at max mechanical advance, where does the idle fall?

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sun Aug 09, 2015 3:29 pm

Yeah I know all about the hole.
Is this thing on?
So far I've gotten the timing at full advance and idle to line up, 5btdc I forget. I'm gonna go drive to Sluggo's and see how it goes. Haven't checked the throttle plate yet, bet the hole is there. She said that too.
If the ** stays dialed in this time, I only have to deal with the rich coming off idle, not thrilled with that lil puff of black.
It really does seem like the carb is fighting me, but in odd subtle ways. It is not behaving. True too I am learning all about this retard nonsense. I have also messed with the settings so much there is no baseline anymore. It seems to be behaving, I will certainly report back. I have confidence in the distributor it seems to run very nicely.
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http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Mon Aug 10, 2015 3:52 pm

Drove all over town last night, it didn't die once even off the freeway. Runs well. Maybe a bit thirsty but it would explain a bigger engine.
It is also louder than my other engine, who knows maybe a funky old muffler. It is good enough. It is certainly peppy.
Thank you for all the advice, it seems to be there now. The fast idle screw hardly engaged + a really far out idle air screw was the winning setting.
It is also interesting how much worn Bus1's front end is...steering box, center pin etc. It is quite a difference oh well I'm too broke for that.
http://greencascadia.blogspot.com
http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
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asiab3
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Mon Aug 10, 2015 6:43 pm

Well I'm glad it's starting to work.

Would you believe it that yesterday after the swap meet, my engine wanted to drop RPMS and take a dump during braking in neutral/ pulling up to stop lights? I installed the 1970-only idle cutoff solenoid gasket, ad it sealed up a vacuum leak I didn't know I had. I had to lean the idle mixture way out to make the idle happy again. So as soon as I installed that part, my mixture went pix rich at idle…

Soooo that begs the question: how do you know "The engine seems to be happiest at slightly rich at idle"?

Can you get it "happy," screw the mixture screw in all the way, COUNTING THE TURNS, (for recall,) and try driving it 1/4 turn leaner. Then another 1/4 turn leaner, until you get a difference in drivability? If the proverbial bucket is fudged, you have your turn counts to reset back to current mixture settings.

I like to experiment with this stuff, I learn well that way. Hell, I bought a now-paperweight Mallory SVDA distributor to experiment with timing maps, economy, and drivability. Want to know what I learned? The factory SVSA is better than anything I could cook up with "theory"…

How is the fuel level in the carb? I had a wonky return-to-idle in a friend's car, until we found two thick washers under the needle valve, rendering the fuel level significantly lower than what the engine wanted.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Amskeptic
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Re: Issues with Type1 Dual Port - Idle

Post by Amskeptic » Fri Aug 14, 2015 1:23 pm

hambone wrote:The fast idle screw hardly engaged + a really far out idle air screw was the winning setting.
Fast idle screw is serving exactly the same function as the throttle stop screws on the dual PDSIT carbs, it prevents the throttle plate edges from goring the venturi. You can set the fast idle screw to just contact to 1/4 turn past contact.

Up above, did your post say that you had the idle timing at 5* ATDC or btdc?
To let the carb pass plenty of air at idle, it should be after, then the transition to the main jet is a smooth experience. You can have a pig rich idle and a lean highway, by the way, see above "transition".
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Fri Aug 14, 2015 2:24 pm

Yeah it is ATDC I goofed.
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http://pdxvolksfolks.blogspot.com
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asiab3
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Fri Oct 09, 2015 8:58 am

Continued from another thread...
hambone wrote:Having trouble with this DVDA. Mebbe the Mexican carb too. Best I can do seems to be 30 deg. full advance, then I have to disconnect the retard. If I run it at 32 full advance the retard (barely) barely keeps the idle at 900. If I run it at 28 deg. it doesn't like to idle after a run, and runs hot.
It also doesn't like to start after warm and shut off. I have to crank it a good 6-7 seconds before it catches, pedal floored "the Colin method".
When cold it runs rough for the first minute or so. I don't like it but it's the way it's been.
Hard to tell what to do, if it's the carb or the distributor. I've been chasin my tail here for a month. It seems to like higher advance...
When you say "full advance" do you mean mechanical AND vacuum? Or mechanical only, with hoses off?

Do you remember off hand seeing the hole in your throttle butterfly plate? DVDA distributors like this hole, and some carb rebuilders (Volkzbitz if you ask him to) will solder/rivet this hole shut to make it better with a 009/SVDA.

Is your big idle speed screw cranked WAY out? Good! You have my permission to really loosen it to get an idle. As long as the screw o-ring is still stiff enough so the screw doesn't back out, 'yer fine.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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