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Too Much Vacuum At Idle - 30PICT1 and 205K
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67_Deluxe
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PostPosted: Mon Aug 10, 2020 11:10 pm    Post subject: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

I wouldn't have thought timing my 67 Bug would be such an enormous headache.

I did a full tuneup on the car - rebuilt 205K distributor, points, & vacuum can, rebuilt 30PICT1 carb from Volkbitz, set the valve clearance, oil change, blew out idle jet with compressed air, the whole nine.

I had some trouble isolating the problem for why the car wouldn't idle properly, but I finally chased it down with a digital timing light and some sleuthing.

All the threads I've read on TS have advised that there shouldn't be much - if any - vacuum at idle. When I do the following on a warm, warm, warm, engine:

1. Statically time the distributor to 7.5 BTDC with a continuity tester;
2. Remove distributor-side vacuum tube and plug hole (while other end is still in carb);
3. Hit the pulley with timing light set to 7.5 BTDC;

Everything looks good. The pulley hits at TDC with the light, indicating that it is indeed at 7.5 BTDC. I use the (only one screw on the 30 PICT 1) fuel screw on the carb to set the idle to 875RPM on the timing light's digital tach (it bounces around from 850-890 RPM).

Here's the question: If there shouldn't be much, if any, vacuum coming from the carburetor at idle, then why does timing jump all the way to 15 BTDC as soon as the vacuum line is reinserted into the distributor's can? As you probably already guessed, the RPMs also increase to 1000. When under load (3000-3500 RPM), distributor still produces 32-ish total advance, however, at idle something (the carb?) is adding 7.5 additional degrees of advance.

I think other posts have already answered my question that this much advance at idle shouldn't be occurring from the vac line, but if I'm wrong about that then please let me know. What I think I'm supposed to be asking here is: what could be causing this problem? Pertinent - and not so pertinent - information below.

Engine:
1500 SP Case (original to car), pistons bumped to 85.5 during rebuild in 2014 (so it's a 1600 now).

Current compression numbers
Cyl 1: 153psi
Cyl 2: 155psi
Cyl 3: 152psi
Cyl 4: 164psi

Distributor:
model -205K
points set to 48 on dwell meter

Carburetor
Western German 30 PICT 1 (105-1 on the flange), rebuilt by Volkbitz

Spark Plugs
Beru 175/14 NOS, gapped.

Any help would be greatly appreciated.
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heimlich Premium Member
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PostPosted: Tue Aug 11, 2020 1:13 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Please take a picture of the distributor and vacuum can. If the wrong can is on there it can cause issues.

Can you put a vacuum gauge on the carb to see what pressure it is pulling at idle?
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PostPosted: Tue Aug 11, 2020 2:27 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Even though your engine is warmed up, is the choke butterfly fully open (vertical)? If the choke butterfly is even partially closed it will create more vacuum in the venturi area which translates to more vacuum to the left side vacuum advance port.

The other possibility I can think of is the venturi vacuum port in the carb throat is plugged. This forces the vacuum to come from only the lower vacuum source which has a stronger vacuum. Check this by squirting carb cleaner into the left side vacuum port and see where is comes out from. You may need to take the carb off the manifold to see where cleaner is coming out from in the lower portion of the carb. If cleaner only comes out from a lower port (below the closed throttle plate) it explains the high vacuum at idle.

See the below table which maps the amount of vacuum required to get degrees of timing advance.
Image may have been reduced in size. Click image to view fullscreen.

According to this table you need 28mmHg (1.1inHg) before the vacuum canister raises the timing by 7.5deg.
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67_Deluxe
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PostPosted: Tue Aug 11, 2020 7:02 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

ashman40 wrote:
Even though your engine is warmed up, is the choke butterfly fully open (vertical)? If the choke butterfly is even partially closed it will create more vacuum in the venturi area which translates to more vacuum to the left side vacuum advance port.

...

According to this table you need 28mmHg (1.1inHg) before the vacuum canister raises the timing by 7.5deg.


Excellent info. Thank you. Ill pull the carb and do these tests - will update the thread afterward.
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PostPosted: Tue Aug 11, 2020 8:33 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Actually, reading the table a second time... it is a range of vacuum that could result in 7.5deg. It is between 28mm ~ 42mmHg.
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67_Deluxe
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PostPosted: Tue Aug 11, 2020 11:32 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Carb pulled, venturis clear all the way through, plate angle looking ok as well. Still searching for the culprit.
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PostPosted: Wed Aug 12, 2020 3:30 am    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

I was trying to post a detailed response to this hours ago, but either I hit a wrong button or something glitched and it got lost and I didn't feel like going over it again.

I have demonstrated how having the lower advance drilling in the wrong spot relative to the throttle butterfly will throw this all out of whack. I would not expect to see this on a stock carb, but I guess it's possible. My experience was the first generation of EMPI brand knockoffs.

https://www.thesamba.com/vw/forum/viewtopic.php?t=278191

A couple of comments. Originally some 66 30PICT-1 owner's manuals still specified the previous 550RPM idle speed. This was soon changed to 700-800RPM. Later to 750-900. If this is a single port engine, it should easily be handle lower speeds, you might just go with 750RPM and see how it works.
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PostPosted: Wed Aug 12, 2020 5:57 am    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

67_Deluxe wrote:
Carb pulled, venturis clear all the way through, plate angle looking ok as well. Still searching for the culprit.

Can you clarify what you mean by the above? Did you try squirting carb cleaner into the left side port and confirm cleaner came out from both the venturi area opening and the lower opening at the throttle plate? Here is a pic from glutamodo showing both ports:
Image may have been reduced in size. Click image to view fullscreen.


Take a look at his link above. It describes the different vacuum/rpm levels from various model 30Pict1 carbs. glutamodo is the Solex Pict carb guru. Listen to his advice.
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PostPosted: Wed Aug 12, 2020 6:51 am    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

I would reach out to Tim...But look at Andy's thread on the carbs...might have plugged port. Tim's work is amazing, but maybe he missed something..
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PostPosted: Wed Aug 12, 2020 12:35 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

67_Deluxe wrote:
I use the (only one screw on the 30 PICT 1) fuel screw on the carb to set the idle to 875RPM


That's not how idle speed is adjusted on 30 PICT-1 carb. You use the screw on throttle lever.
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PostPosted: Wed Aug 12, 2020 2:06 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

kreemoweet wrote:
67_Deluxe wrote:
I use the (only one screw on the 30 PICT 1) fuel screw on the carb to set the idle to 875RPM


That's not how idle speed is adjusted on 30 PICT-1 carb. You use the screw on throttle lever.


That's an interesting take - you'd be the first to say that from what I've read and heard, but I'll consider it. Jay Salser (also a Samba member) has a really good write-up on how to set the idle on the carb here (http://1967beetle.com/carb-installation/) it may be worth a look when you get a chance.

I put a vacuum meter on the carb vacuum and it reads 45-50 mmHg at idle. When I put load on the engine (3000-3500 rpm), the vacuum from the carburetor read 155 mmHg. Going by the graph posted by Ashman40, I'm trying to figure out if the carby shouldn't be producing that much vacuum under load or if it's just on the high end of its plateau-limit.

Seems that is, indeed, the problem (unless it's possible the advance plate on the distributor 'moves TOO freely?' but I don't think that's actually a thing).

So it seems we are certain the problem lies in the carburetor - please share your thoughts if you feel differently. I will spray carb cleaner into the Venturi port and see if its clogged.
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PostPosted: Wed Aug 12, 2020 2:26 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

67_Deluxe wrote:
That's an interesting take - you'd be the first to say that from what I've read and heard, but I'll consider it. Jay Salser (also a Samba member) has a really good write-up on how to set the idle on the carb here (http://1967beetle.com/carb-installation/) it may be worth a look when you get a chance.

The instructions at your link are a bastardised mix of how to adjust a single screw carburetor (28 and 30-1 series) and a two screw carburetor (30-2/3, H30/31, and 34 series), and are incorrect for how to adjust your carburetor. If you don't believe the idle speed screw on your carb is the one in the throttle arm, then you need to read through some factory and service literature.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Wed Aug 12, 2020 3:08 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

mukluk wrote:

The instructions at your link are a bastardised mix of how to adjust a single screw carburetor (28 and 30-1 series) and a two screw carburetor (30-2/3, H30/31, and 34 series), and are incorrect for how to adjust your carburetor. If you don't believe the idle speed screw on your carb is the one in the throttle arm, then you need to read through some factory and service literature.


I not only believe, but have seen the light - I didn't intend the last post as dismissive and appreciate the pics you shared.

I do have a question on the procedure beginning with the "Idle Speed Adjusting Screw:" turn it in how far? I'm not getting where to set the starting position of that screw before moving onto the volume control screw.

Do you think the problem may be resolved by following these procedures?


Last edited by 67_Deluxe on Wed Aug 12, 2020 3:16 pm; edited 4 times in total
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PostPosted: Wed Aug 12, 2020 3:08 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

IIRC I set the timing with the vacuum hooked up to idle at roughly 8-900 rpm and if you pullrf the vacuum line it would idle way slow, This was on a 1300 with 30pict1 and vacuum only distributor. I would get approx 40-42 degrees at 300 rpm.
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PostPosted: Wed Aug 12, 2020 4:10 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

67_Deluxe wrote:
I do have a question on the procedure beginning with the "Idle Speed Adjusting Screw:" turn it in how far? I'm not getting where to set the starting position of that screw before moving onto the volume control screw.

Do you think the problem may be resolved by following these procedures?

There isn't a specific number of turns for the idle speed screw, you simply adjust its position so as to attain the correct idle speed once the engine is warmed up and the choke is fully open. As noted in section 11/39 of the Look and Listen guide, set the idle speed with the adjust screw to the desired speed, then adjust the volume control screw, then readjust the idle speed screw as required to get the idle back where it should be. Initial settings just to get the engine running aside, your final carburetor mixture and idle speed adjustments must be performed when the engine is fully warmed up and not tweaked again when the engine is cold.

Your idle vacuum reading of roughly 40-50mm HG sounds normal for the advance port on a 30PICT-1 given your idle speed, as does the reading of roughly 150mm HG at 3000-3500rpm under no load (revving the engine when not in gear imparts little to no load on the engine, only driving the rear wheels will induce a load). You would likely notice a lower vacuum reading at idle if you lower your idle speed as suggested by glutamodo.

The initial "issue" causing concern where the ignition advances from your static setting as soon as you reconnect the vacuum line is perfectly normal.
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PostPosted: Wed Aug 12, 2020 8:37 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Actually, 40-50mmHG at idle is way too high. Depending on the idle speed but still.

To me is sounds like it's not being properly balanced by the upper venturi fitting.

I linked above to a thread about how early EMPI 30PICT-1 carbs did not provide ENOUGH vacuum at the low end, and it was due to having the lower drilling just a millimeter or two too high. I was able to fix this, but it's all in that thread. However I will pull from that thread, this chart of what to expect for this sort of vacuum advance vs RPM. 40mmHg is a bit high.


Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Wed Aug 12, 2020 8:40 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

I owe a debt of gratitude to everyone on this thread who has helped. You were correct and the "Idle Adjustment Screw" was indeed the culprit.

I think - for posterity (esp. folks checking out this thread in the future) - my takeaway is that step one should be "loosen or remove the barrel nut holding in the throttle cable." In hindsight; a really stupid mistake, but live and learn.

I set the idle speed to 775 RPM and that gives me 8 degrees of advance at idle, but preserves a full band of advance up to 31 degrees at 3500 rpm (I believe that's what it's supposed to be?).

The issue from what I can tell is that the throttle cable was putting too much "tug" on the idling arm, thus creating the vacuum in the carb's throat at idle.

Again, thanks very much to all. The old bug purrs like the day it rolled off the factory line.
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PostPosted: Wed Aug 12, 2020 8:47 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

Wow, throttle cable adjustment. I've talked a lot about various things here over the years, this has come up more than once, but I tend to overlook the possibility.

Me, I usually adjust the throttle cable by a different criteria, Full Throttle, which is laid out in the service manuals.

Image may have been reduced in size. Click image to view fullscreen.


Now, after setting it up that way, I always make sure that the cable still has enough idle slack to make the carb rest properly that way.
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PostPosted: Wed Aug 12, 2020 10:48 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

67_Deluxe wrote:
kreemoweet wrote:
67_Deluxe wrote:
I use the (only one screw on the 30 PICT 1) fuel screw on the carb to set the idle to 875RPM


That's not how idle speed is adjusted on 30 PICT-1 carb. You use the screw on throttle lever.


That's an interesting take - you'd be the first to say that from what I've read and heard, but I'll consider it. Jay Salser (also a Samba member) has a really good write-up on how to set the idle on the carb here (http://1967beetle.com/carb-installation/) it may be worth a look when you get a chance.

There was one line in that write up that I think the OP overlooked....
Quote:
There is a screw at the front-top of the throttle lever... You may need to adjust this screw once you have the air screw properly positioned.

This suggests that once the air screw is adjusted you should use the throttle arm screw to adjust the idle rpm.

I agree that the write up wasn't clear on the use of this adjustment.
The steps posted by mukluk are much better. It is almost never just adjusting the throttle arm screw once and the air screw once. Not uncommon to go back and forth between the two screws a few times.

If you can close the throttle plate as much as possible you may be able to reduce the amount of vacuum advance at idle. You just need the warmed up idle to be just enough to keep the engine from stalling when you come to a stop. If that needs to be 800rpm, so be it. But if you can get it down to 600rpm do that. The more you can close the throttle plate the less vacuum will be on the left side vacuum advance port at idle.

Using the throttle arm screw as the idle adjustment only applies to those carbs without a bypass screw, like your 30Pict-1.
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PostPosted: Wed Aug 12, 2020 11:15 pm    Post subject: Re: Too Much Vacuum At Idle - 30PICT1 and 205K Reply with quote

ashman40 wrote:
There is a screw at the front-top of the throttle lever... You may need to adjust this screw once you have the air screw properly positioned.
This suggests that once the air screw is adjusted you should use the throttle arm screw to adjust the idle rpm.


This was exactly it. It was like a dance - adjust one, adjust the other, wait for the revs to mellow out a bit...adjust back and forth several times until it's dialed in.

Your instructions and Mukluk's were spot on. I wouldn't have known that the issue was the throttle cable unless I took a hard look at the idle screw to see that its position on the cam is relevant to the discussion - and that when I backed off the screw so much that it was no longer on the cam, but the revs and vacuum were still high, something was up in that area.

Andy's input was also helpful in showing me what's going on in this infernal device (the carburetor).

I think it sounds pretty happy now at 775-or-so idle RPM, doubly so since the issue with premature advance has been resolved (it's somewhere between 8 and 9 degrees advance at idle now).

Does 31 degrees max advance sound like it's in the zone of acceptability for this carb/distributor combination? That's the number I'd seen thrown around.
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