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Dual Vacuum Distributor Timing
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vee dub dan
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PostPosted: Sun Jun 19, 2011 8:07 pm    Post subject: Dual Vacuum Distributor Timing Reply with quote

Hi, wanted to make sure from some of you guys that this is the correct way to time a dual vacuum advance distributor..
source
http://www.vw-resource.com/tune-up.html#various

snippet
Quote:
Setting the Dual-Vacuum Distributor with a Strobe
Note: These distributors are timed with both vacuum hoses ATTACHED. If you're not sure which hose goes where, see our article on Dual Vacuum Hoses.

Attach the dwell-tachometer in accordance with the idle procedure above.
Start the engine and allow it to idle at about 900 rpm (if the idle speed is other than this, adjust the idle in accordance with the idle adjustment procedure above).
Point the timing light at the split in the crankcase and pull the trigger on the timing light. When the trigger on the strobe light is pulled, with the engine running, the strobe produces a very bright light which flashes every time the #1 spark plug fires. This bright light is used to observe the relationship between the timing mark on the crankshaft pulley and the split in the crankcase.
Note: When timing the double-vacuum advance distributor (two vacuum hoses), the throttle valve in the carburetor must close adequately for accurate timing adjustment. To check, disconnect the vacuum retard hose (attached to the front of the vacuum chamber and rear of the carburetor) with the engine idling. The timing mark should move 15-18mm to the left. If not, the carburetor needs to be adjusted.


I assume it's trust worthy, but just wanted to double check. Also any tips I should know while doing this? If I remember right, I've done it this way before.. but constant changes have messed it up.

Thanks!
Dan
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PostPosted: Sun Jun 19, 2011 8:11 pm    Post subject: Reply with quote

Yea that's still right.
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ashman40
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PostPosted: Mon Jun 20, 2011 2:44 am    Post subject: Re: Dual Vacuum Distributor Timing Reply with quote

vw-resource.com wrote:
Note: When timing the double-vacuum advance distributor (two vacuum hoses), the throttle valve in the carburetor must close adequately for accurate timing adjustment. To check, disconnect the vacuum retard hose (attached to the front of the vacuum chamber and rear of the carburetor) with the engine idling. The timing mark should move 15-18mm to the left. If not, the carburetor needs to be adjusted.

Just make sure you have the correct vacuum hose connected to the correct port on the distributor.

    Vacuum Retard = Rear Facing port on carb; (larger) horizontal port on vacuum canister on distributor.

    Vacuum Advance = Left facing port on carb; (smaller) vertical port on vacuum canister on distributor.



Those instructions don't actually say it, but you connect the inductive pickup from the timing light to the #1 spark plug wire (cylinder closest to the right front headlight).


The vacuum retard circuit should function at idle. This means if you disconnect the (larger) vacuum retard hose at the distributor while timing with a timing light, you SHOULD see the timing jump to around 7.5BTDC. If there is no change:
- carb adjustment is wrong; not enough vacuum at idle
- vacuum canister is bad and not retarding timing
- wrong carb port is being used; no vacuum at idle

DO NOT set your timing to 5ATDC if the vacuum retard system is NOT working... use 7.5BTDC for a DVDA with a broken retard circuit.
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vee dub dan
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PostPosted: Mon Jun 20, 2011 4:04 am    Post subject: Reply with quote

That's good to know, thank you. I did use a vacuum tester? a friend let me borrow awhile back and everything seemed to check out, but I think just means the vacuum is good and the lines are on correctly. I doubt that the carb is adjusted atm.

While I have this thread going... should all VW's have the same spark plug numbering and location on the distributor cap? We just did a complete rebuild of my brothers bus engine and his 1 & 3 and 2 & 4 are flipped from what mine are.. just thought it was weird, same engine basically but that.
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PostPosted: Mon Jun 20, 2011 5:18 am    Post subject: Reply with quote

vee dub dan wrote:
While I have this thread going... should all VW's have the same spark plug numbering

Cylinder location on all VW aircooled engines is the same:
#1 cylinder = closest to right front headlight
#2 cylinder = closest to right rear taillight
#3 cylinder = closest to left front headlight
#4 cylinder = closest to left rear taillight

vee dub dan wrote:
... and location on the distributor cap?

Location of #1 spark plug wire on the distributor cap differs between distributor models used throughout the years. Other components can also affect where the rotor will point when at TDC for #1 cylinder.


Just remember:
When #1 cylinder will be at the top of it stroke is controlled by the crankshaft and can be identified using the timing marks on the crank pulley being near the case split. The timing marks at this position indicate BOTH #3 and #1 cylinders are at the top of their stroke. One will be at the top of the compression stroke, the other will be at the top of the exhaust stroke. Which one is on which cannot be determined by JUST the crank pulley.

When #1 cylinder will be in its compression stroke is controlled by the camshaft+valves. This is because the camshaft controls when the valves will close, allowing the piston to compress the mixture. You can identify when this is by looking at the valves for #3 cylinder. If the valves for #3 cylinder are moving while the crank pulley timing marks are near the case split, it means #3 cylinder is in its exhaust stroke. That in turn means #1 cylinder is in its compression stroke. The valves for #1 cylinder will NOT be moving because they are closed.

Once you have the engine aligned so #1 cylinder is at the top (TDC) of its compression stroke and ready to fire (based on crank and cam positions).... The distributor rotor WILL BE pointing at the #1 spark plug location on the distributor. This can be anywhere around the distributor, depending on distributor design and other components connecting the crank to the rotor. If everything is setup exactly as it was when the engine left the VW factory, it will be where the factory diagrams indicate. If something has been changed (eg. distributor model; distributor drive gear; key at the bottom of the distributor shaft; etc.) you cannot expect the rotor to point to the same position.
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vee dub dan
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PostPosted: Tue Jun 21, 2011 4:29 pm    Post subject: Reply with quote

Hmm, car is (has been for a little) running hot, at least to me.. I know they get hot but it seems excessive.

Attempted to adjust the idle from the instructions on vw-resources but it keeps dying out at around 900 or less rpm. I unscrewed the bypass alittle to bump it up to around 1000 I think and took it for a drive. It seemed good except sometimes lagging when I hit the gas and sometimes not. Came back and it won't idle without dying now.

When I use the timing light it's killing power to the engine, it was fine on Sunday... so I just do small bursts to make sure it's timed atm. However when I pull the vacuum retard the idle stays at 5atdc, so I guess it's bad. So time it to 7.5 btdc and I'll be able to tell whether it's good or not?

Maybe I should just get a buddy of mine up here to help.. lol I've got so many problems Sad
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PostPosted: Wed Jun 22, 2011 12:58 am    Post subject: Reply with quote

vee dub dan wrote:
When I use the timing light it's killing power to the engine, it was fine on Sunday... so I just do small bursts to make sure it's timed atm. However when I pull the vacuum retard the idle stays at 5atdc, so I guess it's bad. So time it to 7.5 btdc and I'll be able to tell whether it's good or not?

It sounds like you are powering your timing light from the #15 (+) ignition coil terminal. I had the same problem.
Use your battery jumper cables (you do have a set, right) and connect one end directly to the battery and bring the other end out to the engine area. Connect your timing light to the end of the cables. This should prevent the issue of killing your engine while looking at the timing mark.
If you have an alternator (internal or externally regulated... doesnt matter), you can use the large B+ terminal on the alternator as a source for 12v+ (you should get closer to 13v).

If disconnecting your vacuum retard hose does NOT cause a change in idle timing... your retard mechanism is NOT working. DO NOT use 5ATDC as your timing mark. Until you can get it working, set idle timing to 7.5BTDC. Then, with both vacuum hoses disconnected from the distributor, check that you get no more than 30BTDC total (mechanical)advance.
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PostPosted: Wed Jun 22, 2011 3:02 pm    Post subject: Reply with quote

Out of curiosity - exactly what make and model of carburetor are you using here? Aftermarket carbs aren't really set up for DVDA - despite the fact that they have the fitting for it. German 34PICT carbs - if it's got a fitting for the retard line then it's probably set up right inside.

-Andy
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PostPosted: Wed Jun 22, 2011 4:26 pm    Post subject: Reply with quote

glutamodo wrote:
Out of curiosity - exactly what make and model of carburetor are you using here? Aftermarket carbs aren't really set up for DVDA - despite the fact that they have the fitting for it. German 34PICT carbs - if it's got a fitting for the retard line then it's probably set up right inside.

-Andy


And include the flange number if it has one please.
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PostPosted: Wed Jun 22, 2011 5:36 pm    Post subject: Reply with quote

The hole in the throttle plate of the carb will/should be 5/32" for a DVDA and 1/8" for a SVDA.
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PostPosted: Wed Jun 22, 2011 9:37 pm    Post subject: Reply with quote

Pretty sure it's a Holley 34pict-3 from Autozone.... Will double check when I go get it ready for a show tomorrow. About a year after I got it, a couple people here said I should have just rebuilt an old one (or bought a rebuilt one), but oh well.

So this carb probably isn't set up for the DV? I did have a Bosch 009 on it but was told the original dist would be better since the engine is stock.

I had a lot of mixed information from when I got the car compared to what I know now. Definitely learning a lot but still a lot to go.

Where's the flange number...?
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PostPosted: Wed Jun 22, 2011 9:57 pm    Post subject: Reply with quote

Holley 34PICT-3? never seen one of those. The big difference is the size of the hole in the throttle plate - it's larger on DVDA carbs because with the timing cranked way back 12 degrees from SVDA the amount of air flow needed for proper idle adjustment is different. The sizes were mentioned above. Here's a picture:

Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Thu Jun 23, 2011 2:22 pm    Post subject: Reply with quote

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

So it's a Solex 34 pict-3 made in Germany.. Holley must have sold them, which is why I thought that's what it was. Is the second picture the flange number? It was on the right side next to the alternator at the bottom.

I do not see a hole on the throttle plate... is that bad? Embarassed What would symptoms of no hole be? I can probably find a DVDA carb sitting around and swap those plates out.
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PostPosted: Thu Jun 23, 2011 3:04 pm    Post subject: Reply with quote

Wrong base flange number. The one we need is on the other side.

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PostPosted: Thu Jun 23, 2011 3:10 pm    Post subject: Reply with quote

Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Thu Jun 23, 2011 3:18 pm    Post subject: Reply with quote

That is a DVDA style carburetor. Should have a throttle butterfly as shown above. Originally a 1973 California manual transmission model carb - mated with the 113905205AN distributor. It had the older style accelerator pump linkage that interferes with an alternator.
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PostPosted: Fri Jun 24, 2011 12:58 pm    Post subject: Reply with quote

So if the carb is designed for a dvda dist but its not working I assume it's the distributor. I'll try and find a new one this summer..
However what is me not having a hole in the carb throttle plate doing?
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PostPosted: Fri Jun 24, 2011 1:34 pm    Post subject: Reply with quote

There's no hole in your throttle plate? You are looking at the throttle plate and not the choke plate. Did the engine have a 009 in the past? Sounds like this mod was attempted:

http://www.aircooledtech.com/34pict3_modification/

Drill out the hole using a 5/32" drill bit.
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PostPosted: Fri Jun 24, 2011 4:22 pm    Post subject: Reply with quote

Yup looked at the bottom plate going into the manifold and could not see a hole.. I saw a spot where it looks like it goes. The car had a dvda on it when I got it, we put a 009 on and later I bought the new carb and finally recently put the dvda dist. back on.
What does the hole inthe throttle plate do and what would not having one cause (symptoms?)

Also if the vacuum isn't working, since the timing doesn't change when I pull the tubing from the retard end, I don't want to drill a 5/32" hole in this throttle plate until I get a working vacuum?

Going to go pull it apart, make sure there really isn't a hole and maybe just swap it for now.
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PostPosted: Fri Jun 24, 2011 9:01 pm    Post subject: Reply with quote

The hole allows some extra air to bypass the throttle plate, needed when the retard part of the carburetor/distributor is functional - because with the timing cranked back that far, the engine is going to want to idle at a very low speed. That hole allows for proper idle adjustments with the volume and bypass screws on the side of the carb with it at 5ATDC. The SVDA version is smaller becuase it idles at 12 degrees more advance.

Some people will close off that hole to try and make carbs run richer at lower speeds to counteract acceleration flat spots.

-Andy


Last edited by glutamodo on Fri Jun 24, 2011 11:28 pm; edited 1 time in total
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