Vacuum Advance on my Ducellier
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  1. #1
    1000+ Posts Shoji's Avatar
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    Default Vacuum Advance on my Ducellier

    Hi all.
    Why does the Vacuum on my Ducellier dizzy have a small hole?

    It hardly works at all without a sticker over it. It advances lovely with it blocked. You can look at the spring move inside the plastic cover

    Yes your right. I don't what i'm doing.

    But I have this motor running nice tuning it by ear.

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    • Checked manually TDC 1st.
    • Then made the new mark on the flywheel
    • Tuned it by ear at low RPM idle
    • and again at 3000
    • then used the timing light to check on the new mark
    • it is now at + 6~7 degrees.
    • On the old mark it was at + 11~12
    • old motor!!! But now cold - warm starting, running & driving well
    • It now does not smell of unburn't fuel. Yay!!
    • Vacuum Advance on my Ducellier-vacuum-advance.jpg

    “Listen very carefully, I shall say this only once.” Cheers. John

  2. #2
    1000+ Posts driven's Avatar
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    Small hole is to allow the diaphragm to move.

    Probably diaphragm is split. So it is not creating a vacuum to get advance.

    It is only 50 years old.

    Suck on the vacuum hose and you should see the advance move. If not, bin it.

  3. #3
    1000+ Posts Frans's Avatar
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    Hi All.
    I think differently. The hole is on the same side as the vacuum. It would be correct if it was on the opposite side.

    The little hole is a sort of a rough calibration and then the cam on the actual shaft going into the distributer will be a fine calibration. It will suck air through this hole but it is too small to make a difference.

    Remember that it will only advance the timing on the down run. So under acceleration and full throttle there is no advance because there is no vacuum. Lift your foot and there is plenty of vacuum and plenty advance as well. That will assist in burning the lean mixture that would otherwise cause a little backfire. Listen to a G and there is often a little backchat against compression.

    Frans

    PS: under acceleration and full throttle you will rely on the centrifugal weights to do the advance and that will be set to be just enough so that you don't get detonation or pinging.
    Old enough to know better
    Young enough to do it anyway.

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    Quote Originally Posted by driven View Post
    Small hole is to allow the diaphragm to move.

    Probably diaphragm is split. So it is not creating a vacuum to get advance.

    It is only 50 years old.

    Suck on the vacuum hose and you should see the advance move. If not, bin it.
    Also when you suck and it moves stick your tongue on the end of the pipe and it should hold if it doesn't there is a small leak.

  5. #5
    1000+ Posts Frans's Avatar
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    Sunroof,

    It will not hold because of the hole. It is there to cause a leak to reduce the movement of the diaphragm.

    Frans
    Old enough to know better
    Young enough to do it anyway.

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    Quote Originally Posted by Frans View Post
    Sunroof, It will not hold because of the hole. It is there to cause a leak to reduce the movement of the diaphragm. Frans
    That's my understanding too - it is a bit confusing. I guess you need to really sort the advance-retard curve on a bench to know whether it is working really correctly. I also guess most of ours are roughly right and a real failure of driveability is the hint of trouble. The vacuum capsules appear on ebay from time to time.
    JohnW

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  7. #7
    1000+ Posts Shoji's Avatar
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    Well I better take the little sticker off the hole. Lol.
    The diaphragm is holding by the way. I did take the distributor out to tinker/service it and check for any worn parts. seems good.
    I must trust the mechanics of the thing.
    Thank you Frans for putting me straight. I understand but not how to set it properly.
    Should I find someone to check and set the dwell angle 1st?
    I'm starting to think it's an old motor and maybe it's rebuild time? No fumes or oil usage.
    Any decent engine rebuild people in Perth? Another thread.....
    “Listen very carefully, I shall say this only once.” Cheers. John

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    1000+ Posts Frans's Avatar
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    Quote Originally Posted by Shoji View Post
    I must trust the mechanics of the thing.
    Thank you Frans for putting me straight. I understand but not how to set it properly.
    Should I find someone to check and set the dwell angle 1st?
    I would not really care much about the vacuum side of things. If it works it is basically enough. It might advance a little different to factory settings due to old age or others that have fiddled in the past buut remember that this only happens when you are backing off or cruising. You will not have detonation on cruising.

    The main thing to concentrate on is the centrifugal advance of the weights at the bottom of the distributor, below the plate that holds the points. Remove that plate and check the bushes of the weights and that they do not scrape on their base due to worn bushes. If they do then: Remove the small circlips and then the 2 little springs. You can mark them where they are to assemble them the same posiition. If you do not have a lathe to turn new bushes you can use the fiber bushes from old points and put them onto the weights. They go straight on. Lubricate slightly with thin grease. Assemble it all and adjust the points to .018" (thickness of a junior hacksaw blade) and install in the car. The dwell angle should be very close with this gap.
    Start the car and while idling you can set the timing with a timing light to about 8 degrees. Rev the engine slightly and at about 3000rpm the timing must have advanced to about 30 degrees or roughly 30mm on the pulley. This must be done with the vacuum tube removed and blocked. If you get that then you have a good distributer and your timing should be spot on.

    Frans
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  9. #9
    1000+ Posts Shoji's Avatar
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    Quote Originally Posted by Frans View Post
    I would not really care much about the vacuum side of things. If it works it is basically enough. It might advance a little different to factory settings due to old age or others that have fiddled in the past buut remember that this only happens when you are backing off or cruising. You will not have detonation on cruising.

    The main thing to concentrate on is the centrifugal advance of the weights at the bottom of the distributor, below the plate that holds the points. Remove that plate and check the bushes of the weights and that they do not scrape on their base due to worn bushes. If they do then: Remove the small circlips and then the 2 little springs. You can mark them where they are to assemble them the same posiition. If you do not have a lathe to turn new bushes you can use the fiber bushes from old points and put them onto the weights. They go straight on. Lubricate slightly with thin grease. Assemble it all and adjust the points to .018" (thickness of a junior hacksaw blade) and install in the car. The dwell angle should be very close with this gap.
    Start the car and while idling you can set the timing with a timing light to about 8 degrees. Rev the engine slightly and at about 3000rpm the timing must have advanced to about 30 degrees or roughly 30mm on the pulley. This must be done with the vacuum tube removed and blocked. If you get that then you have a good distributer and your timing should be spot on.

    Frans
    I'm going to try this. Thanks Frans!!
    I beleive I have her running well at the moment but there is still a little engine rock at idle when you stare at it. Don't stare at it?
    Would this be because the timing chain, cam, etc are worn? 150.000 miles.

    I thought the dizzy was quite good, no side play in the bushes.
    I used a little chain spray grease on the centrifugal advance mech and it moved well.
    Only when you grab the rotor there is play when you turn it back or forth in the motor.
    Cheers. John
    “Listen very carefully, I shall say this only once.” Cheers. John

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    Quote Originally Posted by Frans View Post
    Sunroof,

    It will not hold because of the hole. It is there to cause a leak to reduce the movement of the diaphragm.

    Frans
    Sorry Frans I don't agree just tried two that work and hold. I believe the hole being referred to is in the back to allow air in and out when the diaphragm moves. True one was a Bosch and the other a SEV perhaps Ducillier are different. I'll try and find a Ducillier and check it.

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    Quote Originally Posted by Sunroof View Post
    Sorry Frans I don't agree just tried two that work and hold. I believe the hole being referred to is in the back to allow air in and out when the diaphragm moves. True one was a Bosch and the other a SEV perhaps Ducillier are different. I'll try and find a Ducillier and check it.
    I think I would have to agree with Sunroof. Having a hole in the vacuum side defeats the purpose of creating a vacuum sufficient to give full movement to the vacuum diaphragm. Every principal I ever learnt on internal combustion engines mandates a complete vacuum for vacuum advance to operate properly. I'll be checking out my Ducellier on the R8 in the morning as I was unaware that the vacuum capsule had a pin hole in it.
    My aircraft engine fitter training taught that vacuum advance was there for initial advance of the spark for initial throttle movement then after that came the centrifugal flyweights to carry the advance through acceleration. Have I been taught wrong ???
    Cheers
    Phil

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    Quote Originally Posted by R8philSA View Post
    I think I would have to agree with Sunroof. Having a hole in the vacuum side defeats the purpose of creating a vacuum sufficient to give full movement to the vacuum diaphragm. Every principal I ever learnt on internal combustion engines mandates a complete vacuum for vacuum advance to operate properly. I'll be checking out my Ducellier on the R8 in the morning as I was unaware that the vacuum capsule had a pin hole in it.
    My aircraft engine fitter training taught that vacuum advance was there for initial advance of the spark for initial throttle movement then after that came the centrifugal flyweights to carry the advance through acceleration. Have I been taught wrong ???
    Cheers
    Phil
    It was also how I was taught Phil. Just tried a Ducillier and it also holds no hole on the suction side.
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    Just spotted your thread. I'm normally on the Citroen sight.
    I've just completed a trip from Brisbane to Castlemaine in a Lt 15 that has had the ID engine conversion. It cruised at high speed but I kept bringing the speed back to 95kph to --- well be sensible.
    On arriving home, I mentioned to my "mechanical" mate that the Lt 15 wasn't happy going around tight roundabouts and traffic through the country towns. It "kangarood" or how will I say. The acceleration isn't smooth until I go through the gears and get the speed up.
    He told me to check the vacuum on the side of the distributor. This I did and sure enough, there's a hissing sound when I suck through the pipe and no movement from the "thingy" inside.
    I'm a bit puzzled that I got such tremendous economy and that it cruised so well with a vacuum/advance that was not operating.
    I've found some spare distributors, so I'll see if I can change the vacuum part that is screwed on the side.
    As you have probably gathered, I don't really have much knowledge of this component but your thread is an eye opener.
    All very interesting ----- Michael Paas

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    I know that we have sort of hijacked this thread so my last comment. Photo shows the method of adjusting vacuum advance on SEV, Ducillier, and Bosch.

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    Default Hmm ??

    Quote Originally Posted by R8philSA View Post
    I think I would have to agree with Sunroof. Having a hole in the vacuum side defeats the purpose of creating a vacuum sufficient to give full movement to the vacuum diaphragm. Every principal I ever learnt on internal combustion engines mandates a complete vacuum for vacuum advance to operate properly. I'll be checking out my Ducellier on the R8 in the morning as I was unaware that the vacuum capsule had a pin hole in it.
    My aircraft engine fitter training taught that vacuum advance was there for initial advance of the spark for initial throttle movement then after that came the centrifugal flyweights to carry the advance through acceleration. Have I been taught wrong ???
    Cheers
    Phil
    I thought that the vacumn advance should not have a hole in the system also. But there is a nagging idea in the back of my head though that I might have seen it somewhere before There is plenty of vacuum to go around if the hole is only small.

    The theory of the advance as i understand it is this; The centrifugal advance is there to get the spark going earlier as the revs go up so the overall burning average pressure is kept at the optimum time. It is restricted as the turbulence of speed takes over and does the same job after a while.

    But the vacumn advance is there because the reduced cylinder pressure as the throttle closes reduces the burning speed so more advance is needed to compensate. It also makes the efficiency much better and improves the fuel economy by a lot The two are independent and add together.

    For interest I had something to do with early Fiats also and they never had any vacumn advance, till the pollution regs came around. Good goers but not nearly as good as Froggies for fuel economy. Not sure what that says about national caracteristics
    Jaahn
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  16. #16
    1000+ Posts Shoji's Avatar
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    LOL.
    To Vacuum or not to Vacuum. This is the question....
    The sticker is coming off the hole. I'll give it a try.
    I imagine the vacuum performs the way it should with the throttle off while driving.
    But not while staring at it and giving it thrash. John
    “Listen very carefully, I shall say this only once.” Cheers. John

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    Default To vacuum or not----

    Hi this discussion brings back snippets of things !! It can be a difficult process

    The vacuum advance port is usually above the throttle plate so it does not advance till the throttle is opened "a bit". That is called over ported.
    However some cars had it under the throttle plate, under ported and the timing had to be set with the engine running. Also the under port may be used for other things too.
    Perhaps the Ducillier used an under port but the hole prevented the advance getting vacuum untill the engine started ?? A cheap and simple effect which sounds likely for them.

    After the pollution rules started to come in the combination of ports and diaphrams and things escallated by a factor of 10 at least. Some dissys had vacuum advance and retard. Who knew how most of them worked. Most people threw it all away. EFI fixed most of that crap.
    Jaahn
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  18. #18
    1000+ Posts Frans's Avatar
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    Hi All,

    Sunroof, all the distributors with holes in the housing I've seen has the hole on the vacuum tube side. I agree that the ones with no hole, will hold, but the question from Shoji was: "why is there a hole?" That hole will be on the vacuum side and it will not hold as seen in the pictures.
    The cam on the shaft that goes into the distributor is for more calibration as in your pictures and as I said in post#3. I agree fully. Have a look at my pictures, maybe my explanation wasn't that good but I will take a side bet that it will not hold the vacuum if you suck it and block it with your tongue. The hole is small so the vacuum from the manifold will easily overcome that leak.





    Regards Frans.
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    Fellow Frogger! R8philSA's Avatar
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    Quote Originally Posted by Frans View Post
    Hi All,

    Sunroof, all the distributors with holes in the housing I've seen has the hole on the vacuum tube side. I agree that the ones with no hole, will hold, but the question from Shoji was: "why is there a hole?" That hole will be on the vacuum side and it will not hold as seen in the pictures.
    The cam on the shaft that goes into the distributor is for more calibration as in your pictures and as I said in post#3. I agree fully. Have a look at my pictures, maybe my explanation wasn't that good but I will take a side bet that it will not hold the vacuum if you suck it and block it with your tongue. The hole is small so the vacuum from the manifold will easily overcome that leak.





    Regards Frans.
    Well, this is certainly confusing. I have a spare Ducellier of a R12 in my shed and I know it is in very good condition. So I just went out and connected a small plastic vacuum hose to the Vacuum capsule and sucked on it, then put my tongue over the hose and it held vacuum for ages. Naturally the points moved a fair amount also. Your right, the little pin hole is definitely on the vacuum side of the capsule and I can't work out for the life of me why air doesn't come through the pin hole and lessen the vacuum.
    So it will remain a mystery to me but if I had another spare vacuum capsule I would cut it in half and answer my own question!!
    I'm very keen to solve this mystery, so I'm all ears . Phil

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    I'm with Frans. The hole on the vacuum side, FOR THOSE SET UP THAT WAY, I think allows the advance/retard to come back faster as the vacuum diminishes but remains, nonetheless, vacuum, with opening throttle. So the return springs work. I guess you could do it differently, for example with stronger return springs.

    Air does come through, but the system has plenty of capacity to suck through and maintain vacuum for a given throttle opening. Remember, we suck for a short time, but the engine is running.

    Many ways to skin a cat.

    There's a lot to be said for efi.
    JohnW

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    It may interest some to know that Alconi Developments recommended that the vacuum advance pipe be sealed off at the carburettor, on their conversions.

    Henry
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    I have now found a Ducellier with a hole and one without. The hole was .6mm.The vacuum unit with a hole did not hold and it took a fairly hard suck to get it to move. The one without a hole was easier to move and held. I wonder what comes off which car? I guess with a dizzy number Simon could tell us. These dizzys of mine are stored away and rather difficult for me to get at, but I'll see if I can find more and record the number against those with and without holes. The advance graph will be interesting. If I have a faulty one I'll split it open and see what gives. I wonder if I ever tossed one because it didn't hold.
    Last edited by Sunroof; 12th March 2016 at 08:16 AM. Reason: spelling

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    Quote Originally Posted by rubyalpine View Post
    It may interest some to know that Alconi Developments recommended that the vacuum advance pipe be sealed off at the carburettor, on their conversions.
    Henry
    Henry,
    As has been said the vacuum advance is only working when you are off the throttle anyway so for performance it is immaterial.
    And if you have big carbies fitted then who knows what the vacuum at any port is going to be, except it will be low !! So it was normal to disregard it.
    On the old VW engines, 36, 40 HP etc they only had vacuum advance, no centrifugal, no weights, but it was double ported, over ported and venturie ported and they acted together to give the advance curve required for all needs. So there is another way to "skin the cat".
    Cheers Jaahn

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    You would not normally run vacuum advance with two by two barrel Webers. Perhaps on a R12G. Hence the need for a large advance setting figure and the high idle RPM.

    Doesn't the dual system like you describe on the VW cause an advance from one suction pipe and retard from the other? Depending on the balance between the two different suction pipes?

  25. #25
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    Complication plus
    There is a guy in Caboolture in Qld that knows his stuff. Haven't used him for years though

    Back to my performance people files I have kept

    Distributor advance

    This will give better understanding on all the ins and outs
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