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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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 Posted: Thu Jun 08, 2023 11:29 am Post subject: Idle issues caused by vacuum leaks in the Autostick CV? |
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Need to ask the collective, anyone have issues with setting the idle on an Autostick that was a result of a leak in the CV?
I have a rebuilt 34-3 from VolksBitz set as suggested, and the engine has a hard time getting the RPMs up to 850/900, and lopes up/down. I suspect a vacuum leak, and tested the carb, replaced the boots, manifold gaskets and the carb base gasket...
The AS 12mm hoses all replaced as well as the small line from the carb.
Anyone ever have a leak at the CV that caused the idle to have issues?
(I am thinking I will put a plug on the 12mm manifold port to remove that from the equation) |
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mukluk
Samba Member
Joined: October 18, 2012
Posts: 7028
Location: Clyde, TX
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| Posted: Thu Jun 08, 2023 11:53 am Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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Have you checked your manifold vacuum with a gauge to see if it's low?
Have you tried disconnecting and capping the vacuum line fittings on the intake manifold and carburetor to see if that changes your idle problem?
Have you run through a full tuneup adjustment procedure to make sure you don't have a tuning issue causing the problem?
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Thu Jun 08, 2023 12:05 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| mukluk wrote: |
Have you checked your manifold vacuum with a gauge to see if it's low?
Have you tried disconnecting and capping the vacuum line fittings on the intake manifold and carburetor to see if that changes your idle problem?
Have you run through a full tuneup adjustment procedure to make sure you don't have a tuning issue causing the problem? |
I have capped the manifold elbow port, plugged the retard line, though not the advance port. All tune up items (valves, cap/rotor/points/condenser, plugs and wires) all new and or checked.
where do you check the manifold vacuum from? |
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mukluk
Samba Member
Joined: October 18, 2012
Posts: 7028
Location: Clyde, TX
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| Posted: Thu Jun 08, 2023 12:34 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| Quote: |
| where do you check the manifold vacuum from? |
From a vacuum port on the intake manifold or a manifold vacuum source on the carburetor. A clear picture or two of your carburetor and intake manifold would help if you need more precise guidance.
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Thu Jun 08, 2023 1:22 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| mukluk wrote: |
| Quote: |
| where do you check the manifold vacuum from? |
From a vacuum port on the intake manifold or a manifold vacuum source on the carburetor. A clear picture or two of your carburetor and intake manifold would help if you need more precise guidance. |
I have a standard OEM German 34-3 with the Retard/advance and Autostick ports only. In terms of manifolds, the left side DP endpiece has the vacuum port for the throttle dampener as well as the 12mm LARGE vacuum port for the AS.
if I place my gage on the left endpiece, will that reading be accurate across the system, or mostly left sided?
I might be able to use the fuel evap line (12mm T to small line) and place that on the center manafold line.
what reading should I be looking for?
(update - after sitting overnight I noticed gas seaping out from the carb base) thay is a good reason for this issue...will update as soon as I take a deeper look. |
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vamram 
Samba Member
Joined: March 08, 2012
Posts: 7304
Location: NOVA
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| Posted: Thu Jun 08, 2023 1:38 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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Is this the same issue you had before installing the Volksbitz-restored carb?
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Thu Jun 08, 2023 2:12 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| vamram wrote: |
| Is this the same issue you had before installing the Volksbitz-restored carb? |
Vicktor - good memory! It is similar in terms of not idling properly, however this one is that the volume or air bypass screws dont appear to be making much of a difference in the idle and it lopes.
The car sat for a couple years, and I just got around to replacing the fuel tank, lines and pump. after I replaced the carb from Tim it ran fine until then. |
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VW_Jimbo
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Joined: May 22, 2016
Posts: 9966
Location: Huntington Beach, CA
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| Posted: Thu Jun 08, 2023 2:47 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| JonRich55 wrote: |
Need to ask the collective, anyone have issues with setting the idle on an Autostick that was a result of a leak in the CV?
Anyone ever have a leak at the CV that caused the idle to have issues?
(I am thinking I will put a plug on the 12mm manifold port to remove that from the equation) |
I have worked on well over 30 - 40 autostick cars, when I was a mechanic. They are sweet rides when they are working right, but getting them there is a f’n job!
Yes, the Control Valve can be a source of a vacum leak. Block off the ports running to it and then set the carb up. Reconnect the CV and see what happens.
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Starbucket
Samba Member
Joined: April 30, 2007
Posts: 4025
Location: WA
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| Posted: Thu Jun 08, 2023 3:22 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| Did this issue start with the rebuilt carb. or was it there before? If it was there before and was the reason you had the carb. rebuilt, it's not the carb., did you test the condenser with an OHM meter? there are a lot of bad ones coming from China. |
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Thu Jun 08, 2023 3:47 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| VW_Jimbo wrote: |
| JonRich55 wrote: |
Need to ask the collective, anyone have issues with setting the idle on an Autostick that was a result of a leak in the CV?
Anyone ever have a leak at the CV that caused the idle to have issues?
(I am thinking I will put a plug on the 12mm manifold port to remove that from the equation) |
I have worked on well over 30 - 40 autostick cars, when I was a mechanic. They are sweet rides when they are working right, but getting them there is a f’n job!
Yes, the Control Valve can be a source of a vacum leak. Block off the ports running to it and then set the carb up. Reconnect the CV and see what happens. |
Thanks, Jimbo! I just need to plug the 12mm line and see how it runs. |
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Thu Jun 08, 2023 3:49 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| Starbucket wrote: |
| Did this issue start with the rebuilt carb. or was it there before? If it was there before and was the reason you had the carb. rebuilt, it's not the carb., did you test the condenser with an OHM meter? there are a lot of bad ones coming from China. |
I ran well after the carb was rebuilt. I had my OEM one rebuilt by Tim because the BOCAR one was leaking through the throttle shaft.
Would a bad condenser cause idle issues? |
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Starbucket
Samba Member
Joined: April 30, 2007
Posts: 4025
Location: WA
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| Posted: Thu Jun 08, 2023 3:55 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| JonRich55 wrote: |
| Starbucket wrote: |
| Did this issue start with the rebuilt carb. or was it there before? If it was there before and was the reason you had the carb. rebuilt, it's not the carb., did you test the condenser with an OHM meter? there are a lot of bad ones coming from China. |
I ran well after the carb was rebuilt. I had my OEM one rebuilt by Tim because the BOCAR one was leaking through the throttle shaft.
Would a bad condenser cause idle issues?
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It will cause weak spark so yes. |
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sb001
Samba Member
Joined: May 19, 2011
Posts: 10406
Location: NW Arkansas
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| Posted: Thu Jun 08, 2023 4:46 pm Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| JonRich55 wrote: |
| In terms of manifolds, the left side DP endpiece has the vacuum port for the throttle dampener as well as the 12mm LARGE vacuum port for the AS. |
Hold up, what??
EDIT: Reading it again I think you are just saying your manifold has the throttle dampener port on the left side end piece as well as the 12mm autostick port on the neck.
The way you wrote that makes it sound like both were on the left side end piece, which would be an issue.
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Fri Jun 09, 2023 6:12 am Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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| sb001 wrote: |
| JonRich55 wrote: |
| In terms of manifolds, the left side DP endpiece has the vacuum port for the throttle dampener as well as the 12mm LARGE vacuum port for the AS. |
Hold up, what??
EDIT: Reading it again I think you are just saying your manifold has the throttle dampener port on the left side end piece as well as the 12mm autostick port on the neck.
The way you wrote that makes it sound like both were on the left side end piece, which would be an issue. |
True, my sentence structure wasnt the best...though I think those who know about the AS understand the 12mm would be on the intake manifold. |
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Tom K.
Samba Member
Joined: March 10, 2005
Posts: 1605
Location: Central Pennsylvania
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| Posted: Fri Jun 09, 2023 9:03 am Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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I'm constantly messing with my idle on my autostick also with recently rebuilt carb and dizzy. I found this simple process helpful for eliminating an ordinary vacuum leak as the culprit (from Ashman).
"If your timing is good, then I too suspect you have a vacuum leak. The tell-tale sign is that the choke masks the problem. While the choke is ON it runs the engine rich. This compensates for the extra air leaking into the intake flow from the vacuum leak. Once the choke is OFF the idle mixture thru the carb returns to normal but the air leaking into the intake results in a lean mixture and the engine struggles/dies.
A simple test for this...
Warm up the engine until the choke is OFF.
Manually rotate the fast idle cam to one of the steps until you can just barely keep the engine running (1500rpm?).
With the engine idling, cover 50% of the opening of the carb with your flat hand to block off the air flow.
Slowly move your hand to cover more and more of the carb opening. At some point you will start to restrict the air flow and you will choke the amount of air allowed into the carb. Normally, this would be the same as closing the throttle plate to reduce the air flow and the idle rpms should go down. Listen to the engine as you choke off the air flow. Does the engine instead run better and the rpms go up? This suggest the engine was running lean and by choking off the air flow down the carb you are balancing the mixture and the mixture moves closer to ideal air-fuel mixture (stoichiometric) so the engine runs better/smoother.
Now you know there is a leak, finding it is the challenge. Use some carb cleaner spray while the engine is idling (using the fast idle cam). Attach the red straw and spray common leak spots. All the rubber connections (intake, hoses), seals (gaskets below the carb and at the heads), carb opening (throttle shaft bore). If there is any change in the rpms when you spray you have found a leak into the air flow. Fix this leak."
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JonRich55
Samba Member
Joined: April 06, 2018
Posts: 378
Location: Leesburg, VA USA
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| Posted: Fri Jun 09, 2023 10:28 am Post subject: Re: Idle issues caused by vacuum leaks in the Autostick CV? |
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Thanks Tom! (It's been a while)
I replaced the carb today with a BOCAR one I modified for use with an AutoStick. I had used this one before I had Tim rebuild my OEM one. It wasnt idling either (when I pulled it off a few years ago) and when I checked the tiny pilot jet I found it was totally clogged. I opened that up, cleaned the float bowl and put it on. The car now idles well (although fast) as I just wanted to see if it would change things (and it did). I will now go about resetting everything and get the RPMs and timing readjusted.
I will need to pick up a SVDA as the BOCAR uses the smaller butterfly hole and needs a later version distributer and timed to 5-7.5 BTDC and the proper advance curve.
My main question about the CV causing the vacuum leak is I wanted to know so I could make a 12mm cap to remove it from the equation. testing the boots, manifold and carb base gasket is easier if you know that is the only places that could be in play. Once you throw in the CV, it takes on the multi-headed Hydra problems |
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