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Ignition, vacuum and timing
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Gadwood74
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PostPosted: Sun Jun 13, 2021 5:33 am    Post subject: Ignition, vacuum and timing Reply with quote

76 Conv. FI converted to Carb

As I am new to this world, I read a lot but I am having a hard time figuring the relation between vacuum, timing, etc.

Below are 2 pictures of my wiring and distributor.

Rome recommend me to modify my vacuum so I would get an ADVANCE feature (connect to left side of carb to the lower vacuum can nipple). Still need to test if it is good (membrane / arm moving inside the distributor).

As you can see on the pulley, I only have one mark. My understanding is that it is the 5 degreed advance mark.

I still don't really understand how vaccum affects timing (or vice versa). If I change the vacuum hose as recommended, it is necessary to have the timing redone?

Also, you see how my wires are connected. Is this OK? As mentioned in another thread, I have hesitation only at high speeds.
- I don't have icing issues so far (will install heat risers shortly)
- My spark plugs are new
- My choke is 100% functional
- I may have cheap ignition wires, just ordered new ones to eliminate this component.

Thanks again for the help.

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Dougy Dee
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PostPosted: Sun Jun 13, 2021 5:52 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

You have 2 marks on your pulley.
TDC is marked on the outer pulley rim.
5degree ATDC is on the inner.
Your pic shows it is at 0degrees or TDC at the case parting line.

Your wiring diagram is wrong. Assuming #1 is in correct location. rotor turns clockwise. Next are plugs 4,3,2 and back to 1. (As indicated on the generator stand base.)
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Gadwood74
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PostPosted: Sun Jun 13, 2021 6:25 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Dougy Dee wrote:
You have 2 marks on your pulley.
TDC is marked on the outer pulley rim.
5degree ATDC is on the inner.
Your pic shows it is at 0degrees or TDC at the case parting line.

Your wiring diagram is wrong. Assuming #1 is in correct location. rotor turns clockwise. Next are plugs 4,3,2 and back to 1. (As indicated on the generator stand base.)


I would need my wires like this then? The car would run almost normally even if ignition wires were wrong? As mentioned, I have misfires at high revs and the car seems slow (slower vs what I remember 30 years ago...)

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frenchroast
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PostPosted: Sun Jun 13, 2021 6:26 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:

I still don't really understand how vaccum affects timing (or vice versa).

The vacuum is what advances the timing in your distributor. If you pull the cap off the distributor and suck on the vacuum tube, you'll see the points plate move/advance. An 009 distributor uses a weight/spring and centrifugal force to advance the plate.


Last edited by frenchroast on Sun Jun 13, 2021 6:45 am; edited 1 time in total
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Gadwood74
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PostPosted: Sun Jun 13, 2021 6:32 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

My wires are 1-4-3-2 since the beginning so I am OK there (my first diagram was wrong, the second one is OK).
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Gadwood74
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PostPosted: Sun Jun 13, 2021 6:34 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

frenchroast wrote:
Gadwood74 wrote:

I still don't really understand how vaccum affects timing (or vice versa).

The vacuum is what advances the timing in your distributor. If you pull the cap off the distributor and suck on the vacuum tube, you'll see the points plate move/advance. An 009 distributor uses a weight and centrifugal force to advance the plate.


When I suck the vacuum tube when connected behind the can, I effectively see the parts moving. But when I suck when connected below, I hear the membrane but nothing is moving


Last edited by Gadwood74 on Sun Jun 13, 2021 6:57 am; edited 1 time in total
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frenchroast
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PostPosted: Sun Jun 13, 2021 6:50 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:

Suck the vacuum tube when connected behind or below the can?

On an sva, there's only one on the front. On a dvda (I think that's what you have) I think it's the front for the advance as well (rear is to retard; someone else will know for sure).
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Gadwood74
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PostPosted: Sun Jun 13, 2021 7:43 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Maybe another idea...

I have a line (look like a brake line) from the canister (rear passenger fender) up to the front fender. Connected to NOTHING!! THen I have this vent from the gas tank connected to nothing (same area). I just figured out they should connect together.

The car is smelling gas since I have it. I really suspect this is the reason.

See the green gas vent line on the picture, this is the one I've connected to the line from the canister.

Would this conduct to misfires and bad fuel pressure/management??

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minimeadow
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PostPosted: Sun Jun 13, 2021 9:15 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

You are correct that part of your gas tank venting system is missing, but this shouldn't lead to any engine performance issues. It is a contributor to the gasoline smell though. If you search this forum for posts on gas tank venting and carbon canister you'll find some info.
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Gadwood74
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PostPosted: Sun Jun 13, 2021 10:41 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Just went for a quick ride after reconnecting my gas tank vent to the canister line.

NO CHANGE! Still have the fuel odors and, as expected, no impact on hesitation.

Gas on the floor on the highway up to 65 mph (max speed) , then after +/- 2 miles, the engine start hesitating. Damn. This is not fun.
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busdaddy
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PostPosted: Sun Jun 13, 2021 10:55 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:

As you can see on the pulley, I only have one mark. My understanding is that it is the 5 degreed advance mark.
Image may have been reduced in size. Click image to view fullscreen.


That mark is 5* ATDC, not before. You need to connect that nipple on the distributor to the port on the LH side of the carb. I also don't see any heat risers on that manifold, that causes big hesitation.
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Gadwood74
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PostPosted: Sun Jun 13, 2021 11:04 am    Post subject: Re: Ignition, vacuum and timing Reply with quote

[quote="busdaddy"]
Gadwood74 wrote:

As you can see on the pulley, I only have one mark. My understanding is that it is the 5 degreed advance mark.

That mark is 5* ATDC, not before. You need to connect that nipple on the distributor to the port on the LH side of the carb. I also don't see any heat risers on that manifold, that causes big hesitation.


It is actually connected from the left side of the carb to the nipple behind the vacuum can (there’s one behind and one on the bottom)

Heat risers will be installed shortly. This would cause hesitation even if there’s no icing on manifold?
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busdaddy
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PostPosted: Sun Jun 13, 2021 12:37 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

It can, the amount of fuel required to overcome condensation in the manifold is much greater when the manifold is cold, hot manifolds keep it in the airstream as a fog, it gets to the cylinders as soon as you open the throttle, not a few seconds later.

the nipple on the can facing the distributor body is the retard port, another cause of big hesitation, it needs to be on the one facing away from the distributor.
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Starbucket
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PostPosted: Sun Jun 13, 2021 12:50 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

What electric fuel pump are you running and where is it mounted? The FI gas tank has two lines, one goes to the aftermarket electric fuel pump the other one needs to be plugged as it was the return line for the FI, so find that line and make sure it is plugged as that's where gas fumes could be coming from.
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PostPosted: Sun Jun 13, 2021 4:39 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:
Just went for a quick ride after reconnecting my gas tank vent to the canister line.

NO CHANGE! Still have the fuel odors and, as expected, no impact on hesitation.

Gas on the floor on the highway up to 65 mph (max speed) , then after +/- 2 miles, the engine start hesitating. Damn. This is not fun.


Please further describe your 'hesitating'. Does it just not accelerate the same? Engine stumble/misfire? Loose power (and unable to keep speed without increasing the throttle)?

Gadwood74 wrote:
Maybe another idea...

I have a line (look like a brake line) from the canister (rear passenger fender) up to the front fender. Connected to NOTHING!! THen I have this vent from the gas tank connected to nothing (same area). I just figured out they should connect together.

The car is smelling gas since I have it. I really suspect this is the reason.

See the green gas vent line on the picture, this is the one I've connected to the line from the canister.

Would this conduct to misfires and bad fuel pressure/management??


This certainly isn't helping the gas smell. That is a really 'cutting corners' way of venting the tank too. Probably leaks/drips gas out that hose I bet.

Be sure that the vent line is not plugged. It would be worth your time/money to replace that venting hose to ensure it hasn't plugged up inside. If your tank is not venting well, then you may have a 'fuel starvation' condition when running at high revs/load/speed. Essentially, the pump is having to pull more fuel, but if the tank isn't vented well the fuel pump has to fight a slight negative pressure/vacuum in the fuel line to pump the fuel and could be unable to pump adequate volume of fuel to keep the carb float bowl full.

To check if your issue is related to tank venting, next time you begin to have the issue, pull over at a safe location and then slowly open the gas tank filler cap- if you hear a 'hissss' or air sound then your tank is not venting well. Also after you open and then close the gas cap again, if your issue is instantly gone for another couple of miles- there is at least part of the issue.

It is not imperative right now to have the entire system intact/functional. First make sure that the fuel tank is venting well...then work on getting the full EVAP system together.

For further information:
Complete Fuel Tank Venting / EVAP System Walk-through


Gadwood74 wrote:
frenchroast wrote:
Gadwood74 wrote:

I still don't really understand how vaccum affects timing (or vice versa).

The vacuum is what advances the timing in your distributor. If you pull the cap off the distributor and suck on the vacuum tube, you'll see the points plate move/advance. An 009 distributor uses a weight and centrifugal force to advance the plate.


When I suck the vacuum tube when connected behind the can, I effectively see the parts moving. But when I suck when connected below, I hear the membrane but nothing is moving



Your vacuum advance side of the distributor can sounds like it has failed. You do not have any vacuum advance (which is REALLY important to eliminate hesitation with the 34PICT3 carbs). Without a functional vacuum can, your distributor is running 'mechanical advance only" (just like the "009" distributor). You will ALWAYS have *some degree* of hesitation with a "009" distributor and a 34PICT3 carb....you can make it better, but it will always be there.

Don't connect anything to the advance side port of the distributor vacuum can, it will only give you a vacuum leak.(and more issues).
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Gadwood74
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PostPosted: Sun Jun 13, 2021 5:32 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

[/quote] Your vacuum advance side of the distributor can sounds like it has failed. You do not have any vacuum advance (which is REALLY important to eliminate hesitation with the 34PICT3 carbs). Without a functional vacuum can, your distributor is running 'mechanical advance only" (just like the "009" distributor). You will ALWAYS have *some degree* of hesitation with a "009" distributor and a 34PICT3 carb....you can make it better, but it will always be there.

Don't connect anything to the advance side port of the distributor vacuum can, it will only give you a vacuum leak.(and more issues).[/quote]

Well I am confused now.

1. I was about to connect the left carb nipple to the bottom of the vacuum can. I should not do it?
2. Do I need to replace this vacuum can as nothing moves in the distributor when I suck it? Is it the distributor that is wrong?
3. If I connect that vacuum, I guess I need to eliminate the other one (as it is now) and cap off those nipples?

Look so easy for you guys, It's just not easy for me to understand all this, so many variables.
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busdaddy
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PostPosted: Sun Jun 13, 2021 5:44 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

If you connect a hose and suck on it does it move?, at least hold a vacuum (suck and cap the hose with your tounge)?, or just flow freely?

If it flows freely the can is broken, if it holds a vacuum it works, unless the breaker plate is stuck.

Here's a big read if you wish to understand that distributor a little better: https://www.thesamba.com/vw/forum/viewtopic.php?t=558307&highlight=distributor
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Gadwood74
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PostPosted: Sun Jun 13, 2021 6:10 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

busdaddy wrote:
If you connect a hose and suck on it does it move?, at least hold a vacuum (suck and cap the hose with your tounge)?, or just flow freely?

If it flows freely the can is broken, if it holds a vacuum it works, unless the breaker plate is stuck.

Here's a big read if you wish to understand that distributor a little better: https://www.thesamba.com/vw/forum/viewtopic.php?t=558307&highlight=distributor


Should I see something move? I hear a membrane, I don't see anything move in the distributor... What is the breaker plate?

But when I suck from where it is now (retard), I see the parts moving in it.
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busdaddy
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PostPosted: Sun Jun 13, 2021 8:08 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:
busdaddy wrote:
If you connect a hose and suck on it does it move?, at least hold a vacuum (suck and cap the hose with your tounge)?, or just flow freely?

If it flows freely the can is broken, if it holds a vacuum it works, unless the breaker plate is stuck.

Here's a big read if you wish to understand that distributor a little better: https://www.thesamba.com/vw/forum/viewtopic.php?t=558307&highlight=distributor


Should I see something move? I hear a membrane, I don't see anything move in the distributor... What is the breaker plate?

But when I suck from where it is now (retard), I see the parts moving in it.

Same parts should move, but in the opposite direction. try giving it a push to see if it's biding on something, it doesn't move much, but it should move.
the breaker plate is the flat surface inside the distributor the points are screwed down to, the arm from the vacuum can gives it a little push or pull and it rotates inside the distributor a bit each way. The pull part is what you need the most.
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PostPosted: Mon Jun 14, 2021 12:59 pm    Post subject: Re: Ignition, vacuum and timing Reply with quote

Gadwood74 wrote:
I hear a membrane, I don't see anything move in the distributor...

When you say, "hear a membrane," do you mean you hear air moving, like the membrane is not air-tight? If the canister will not hold a vacuum then it is broken and will not work as intended.

You can buy used or new-old-stock vacuum canisters to replace yours. Try the classified section of TheSamba.
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