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1972 inconsistent idle
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amikulics
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PostPosted: Sun Dec 31, 2017 4:51 pm    Post subject: 1972 inconsistent idle Reply with quote

I have been trying to get my 1972 bus motor properly tuned and we've gotten it to sound great and make great power but the idle is too inconsistent to drive. I'll add a link to a video of exactly what I mean but it's a 1972 1700 with stock pdsit dual carbs and oil bathe air cleaner. I recently replaced to the throttle return springs with springs I got at home depot, the new springs are stronger than the old ones so I feel fairly certain the throttles are closing fully every time. Also all vacuum lines, plugs, points, valves have been set or replaced. Also I have tried to adjust the idle using the large idle speed screw on the left carb but no matter how much it is turned it does not seem to make a noticeable difference.
It usually idles a little high around 1050 rpm, but without touching anything it will occasionally drop to around 400 rpm and then require the throttle to be opened slowly before it'll sit back at 1050 again or it'll die. It's strange because once its at 1050 it'll usually stay there with no issues until it drops.
What could be the source of the varying idle?

video:
https://youtu.be/bZmPkIW-uj8
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Terminatez
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PostPosted: Sun Dec 31, 2017 5:10 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

I think we have the same problem. Sounds just like mine.

Others suggested testing for vacuum leaks, try that. I haven't had a chance to tend to the issue yet.

https://www.thesamba.com/vw/forum/viewtopic.php?t=690511&highlight=
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Wildthings
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PostPosted: Sun Dec 31, 2017 5:58 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

Have your tried moving your throttle shafts around? Worn throttle shaft bushings are a major problem with these carbs, they create a vacuum leak which throws the idle off, excessive wear also causes the alignment of the throttle plate and various ports to be off. As others mentioned vacuum leaks from hoses and boots are also a very likely problem.
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lil-jinx
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PostPosted: Mon Jan 01, 2018 10:47 am    Post subject: Re: 1972 inconsistent idle Reply with quote

Bit of good info here.
http://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=7767
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PostPosted: Mon Jan 01, 2018 11:29 am    Post subject: Re: 1972 inconsistent idle Reply with quote

Brakevacuum line and hardware often gives you a two cylinder vacuum leak..

But I would guess if you haven’t rebuilt your carb bushings , they are overdue
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amikulics
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PostPosted: Wed Jan 03, 2018 3:19 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

From what I've gathered it seems to be either a bad brake booster hose or the throttle bushings causing a vacuum leak. When I rebuilt the carbs I did not rebush them, I've looked in the classifieds and the only thing I was able to find was someone selling new, rebushed, throttle bodies but they are for a type 3. I know the Type 3s also used PDSIT 32 carbs, would the type 3 throttle bodies be the same as the ones used on the buses? It would be way easier for me to just buy a new set of throttle bodies than try to rebush them myself.
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PostPosted: Wed Jan 03, 2018 3:27 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

The type 3 TB's are too small, you need to contact Tim at www.volkzbitz.com and see if he will repair yours.
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PostPosted: Thu Jan 04, 2018 7:44 am    Post subject: Re: 1972 inconsistent idle Reply with quote

[quote="asiab3"

And just like the 34pic3, the idle circuit (central idle circuit in your case) can mask your throttle shaft wear until you get them professionally rebushed. No need to lose any sleep here unless yours practically rattle.

Robbie[/quote]
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amikulics
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PostPosted: Thu Mar 08, 2018 8:07 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

It has been a while but I still have had no luck with these carbs. I visited jbugs recently and picked up some OEM throttle return springs and I also replaced the entire brake booster vacuum line. As someone else said and as this:

http://www.itinerant-air-cooled.com/viewtopic.php?t=7767

link says the worn throttle shafts should be able to be masked by the central idling system. There must be something else that causes the idle to vary so much, because the shafts cannot move very much. If I start it and warm it up the idle will be happy at around 950 but after about 10 seconds it likes to drop to around 400 and wants to stall, even without me touching it at all. Sometimes when I gas it quickly it will stall immediately. It is very hard to give exact symptoms since it doesn't always behave the same way. I did replace the fuel pump with a new mechanical one, I forget the brand but i know it was not known for its reliability, however it was the only option for a mechanical pump. I'm running out of ideas as to why it won't run right so any help would be appreciated.
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amikulics
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PostPosted: Fri Mar 09, 2018 5:47 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

Today I decided to stop chasing my tail and just restart following amskeptic's instructions. It seems to have solved the varying rpm idle rpm issue but now it wants to stall when the throttle is openned fast. I'll link to two videos that'll give you a better idea of what I mean. Slowly giving gas will raise the rpm no problem and it sounds great, but quickly hitting the gas will make it sputter and sometimes stall. I believe this to be a mixture issue and my novice knowledge of old cars makes me think this is the carbs running too rich. I feel like the motor is almost done but I wanted some direction before turning screws and getting it completely out of whack again.

https://youtu.be/3Xa2pmlZDhs

https://youtu.be/XtIEXAlkPwU
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amikulics
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PostPosted: Tue Mar 13, 2018 8:05 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

Any ideas?
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PostPosted: Tue Mar 13, 2018 8:37 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

amikulics wrote:
Any ideas?
I will preface this by saying that I don’t know these carbs. First make sure that your valves are properly adjusted and that your timing and dwell are correct. Next, and here is where my ignorance of these carbs swill show, try adjusting the accelerator pumps for more squirt and see if that solves your stumble off idle issue. Also, remove your brake vacuum line from the intake manifold and plug the manifold unless you are absolutely certain that you have no leaks on the brake vacuum circuit.
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PostPosted: Wed Mar 14, 2018 2:34 am    Post subject: Re: 1972 inconsistent idle Reply with quote

What distributor are you running?

Should be stock.

Look for the squirt of the accelerator pump jet gas with a mirror in each carb, when you pull the linkage back. Pffft.
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PostPosted: Wed Mar 14, 2018 6:50 am    Post subject: Re: 1972 inconsistent idle Reply with quote

amikulics wrote:
Any ideas?


1) be 100% sure timing is right
2) Verify there are no vacuum leaks causing improper advance under heavy accel
3) Verify you synced your carbs
4) Fuel pump (see amskeptics post)
5) If there is a fuel, try adjusting your pump to lean it out a little. If the leaning it out doesn't help, try richening it. (I'm not convinced that it is going lean)
6) Clean your jets really well. (maybe it is running lean already, so when you give it gas quick it goes super lean and pops)
7) start making up your own theories, they're gonna be as good as any... Once you test everything you can think of, make a list and let us know. Maybe we will be able to help decipher more then.

God Speed.
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amikulics
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PostPosted: Wed Mar 14, 2018 9:32 pm    Post subject: Re: 1972 inconsistent idle Reply with quote

Abscate wrote:
What distributor are you running?

Should be stock.

Look for the squirt of the accelerator pump jet gas with a mirror in each carb, when you pull the linkage back. Pffft.


Yes, we are running the stock distributor with vacuum advance and retard and I checked and both carbs are getting a nice burst of gas. My current theory is the accelerator pumps are maladjusted.Though I'm not sure if they are rich or lean. My plan is going to be to move the little cotter pin to the other slots and see if it helps. I should be able to try this in the next few days and I'll get back to this thread. But what kinds of symptoms or sounds could I watch out for to determine if it is running lean or rich without a CO sniffer?
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PostPosted: Thu Mar 15, 2018 1:37 am    Post subject: Re: 1972 inconsistent idle Reply with quote

What is your timing doing while this is happening? Does removing either of the hoses from the vacuum can change how it runs? Have you tried timing the engine at 28° BTDC @3500+ rpms, hoses off and plugged verses timing it at idle? You can not time the engine correctly at idle unless you get the idle speed down past where it is.
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