DS23 manifold drip tube
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Thread: DS23 manifold drip tube

  1. #1
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    Default DS23 manifold drip tube

    As those who read the thread I recently created about carburation issues with my 1974 DS23 (DS23 BW35 carburation queries)
    will be aware, one of my queries related to the drip tube hose tail installed in the base of the inlet manifold, underneath the carburettor.

    Although I've owned the car for many years, I was unaware of the existence of this device, but having recently spotted it and discovered that it allows un-metered air to enter the inlet manifold, it struck me that this must affect the fuel-air mixture entering the engine and in doing so, influence the tuning process.

    Today I fitted a plastic tube to the drip tube hose tail (I can't remember having seen anything attached to it previously) and attached a vacuum gauge to the other end of the tube.

    The vacuum read a steady 17" Hg at idle (not ideal, I concede) and when I unplugged the gauge, the idle speed increased significantly and the idle became quite lumpy.

    Am I overstating the importance of the drip tube to the tuning process, or has this issue been dealt with extensively in the past, to the extent that it's not discussed any more in Citroen Forum conversations about tuning the D?

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    With the drip tube closed, my mixture adjustment screw is set about 1 turn anticlockwise from its seat, whereas previously it was about 21/2 turns a/c.

    The engine seems less liable to stalling when I engage R - it stumbles a bit when I engage D - but I am yet to road test the car to see how, or whether, driveability has been altered.

    I would be interested to hear others' experiences with the drip tube (I understand that the factory installation was a 400mm open tube connected to the hose tail).

    Chris

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    Sorry Citquery but WTF is a hose tail?

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    It's a fitting to which a flexible hose is attached.

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    I think that you will find that the drain tube fitted to the base of the intake plenum area of the manifold has a carefully sized small hole that has been calculated to not affect the air/fuel mixture at idle by much, and yet still provide adequate draining of the plenum if the carburettor is flooded. TAs have a similar tube. the end of the tube is tapered and has a hole of about 0.8mm in diameter. People make the mistake of replacing a broken tube ( it happens from time to time, usually through carelessness) with a length of plain tube that admits far too much air, or by blanking off the fitting into the manifold, which makes the idle difficult to tune. Thankfully the drain fitted to a D is much shorter and less prone to damage, being hidden under the manifold.
    Cheers Gerry

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    The concept of a small hole which allows excess fuel to escape - without admitting too much air - makes sense, Gerry.

    My reference to the length of tube attached to what I describe as the hose tail came from this thread, the second post of which includes a good photo of the fitting (without tube): DY3 motor, rubber hose under intake manifold?

    I don't have the 648 manual so I'm not sure whether it shows the specific details of the tapered tube you describe.

    Any further detail would be much appreciated.

    Chris

    PS I have now sourced a 648 manual. The parts diagram doesn't shed much light on the drain tube, but it is described as "5 x 7 x 400", 5 or 7 (mm) presumably being the internal diameter of the tube and 400 (mm), its length. C
    Last edited by Citquery; 5th January 2020 at 07:43 AM. Reason: further information

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    Hi
    Those are my photos in the other thread. They show the manifold of my DS21 - so a DX rather than a DY3.

    The hose tail screwed in the bottom has a barb of sorts to grip the push-fit tube. The dimensions of the tube are given in the manuals - including section 2-141 of 648. 400mm long, OD of 7mm, ID of 5mm. No taper. I can confirm that from the hardened tube I removed and replaced.
    tube.jpeg
    1968 DS21bvh Pallas in Gris Palladium

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    Quote Originally Posted by Budge View Post
    Hi
    Those are my photos in the other thread. They show the manifold of my DS21 - so a DX rather than a DY3.

    The hose tail screwed in the bottom has a barb of sorts to grip the push-fit tube. The dimensions of the tube are given in the manuals - including section 2-141 of 648. 400mm long, OD of 7mm, ID of 5mm. No taper. I can confirm that from the hardened tube I removed and replaced.
    tube.jpeg
    Maybe no taper on later cars but definitely there on DS and ID 19
    Cheers Gerry

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    I'm also confused now Gerry. Do you mean that the internal diameter of the 400mm tube changes over it's length, or do you mean that the metal fitting on the manifold is tapered to grip pipe that is fitted to it? If the taper on the tube, and this waswas an intentional design thing, then why not continue it on later cars?
    1968 DS21bvh Pallas in Gris Palladium

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    Quote Originally Posted by Budge View Post
    I'm also confused now Gerry. Do you mean that the internal diameter of the 400mm tube changes over it's length, or do you mean that the metal fitting on the manifold is tapered to grip pipe that is fitted to it? If the taper on the tube, and this waswas an intentional design thing, then why not continue it on later cars?
    Budge , I am talking about the metal fitting next to the union for the manifold pre heat hose which runs from the water pump. I have checked my references and it is plain now that this metal fitting is not the same as the early cars 1911 cc engines plenum drain. It appears to have a constant bore and the flexible rubber tube fits onto it to carry flooded fuel well down into the engine bay depths. So I apologise for my confusion between the early type and that fitted to the carburettor equipped short stroke Ds.
    Cheers Gerry

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    Actually, I just checked my CX2400 and the setup with the drain tube is exactly the same. It has the short metal tube with the barbed end to take a length of tubing.
    Cheers Gerry

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    Budge and Gerry, thank you for expanding on this topic. I understand the concept of draining excess fuel from the inlet manifold, but I find Citroen's approach somewhat perplexing.

    To fit a mini-vacuum cleaner hose to the underside of the inlet manifold seems bizarre from at least two perspectives. Firstly, as you have no doubt noted, tuning the Weber 28-36 DMA5 twin throat carby fitted to the DX engine entails delicate adjustments to airflow - via the throttle plates and air adjustment screw - then they allow this extra inflow of air from the inlet valve side of the carby (together with more air from the crankcase breather)! I understand that the carby adjustments for fuel and air are made while the other (non-adjustable) air inflows are occurring, but to me there's an element of inconsistency to this approach.

    The greater concern - for those of us who travel on dusty rural roads - is that "the mini-vacuum cleaner hose", assuming it dangles 400mm down from the inlet manifold, ends up next to the chassis rail. It's also very close to the nearside front tyre: a perfect spot to suck up fine dust thrown up by said tyre! Much less a problem on sealed roads, of course.

    I think I might stuff some stainless steel wool into the end of the drain hose, with a view to restricting dust ingress and somewhat restricting air inflow.

    Thank you again for your help on this topic.

    Chris

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    Hi
    These musings are from quite a few years back so may be a bit hazey I do recall drain tubes that had a swagged end that made a small hole to control the fuel flow and the air also. They were metal and had no flexible tube on them.
    But when things moved on the drain tube idea might have been thought to dump the fuel on a possibly hot exhaust so they put a flexible tube to carry it further down away from the exhaust. Note another control method for fuel pooling in the manifold was to fit spring loaded needle tips which worked better as they became worn. So avoiding the fuel overflowing out of the jets/bowl.
    So it is essential to get some equivalent hole in the tube or nipple as fitted originally. I would not be so worried about the air(and dirt) that comes in if it is minimal as designed. Because the air flow is reduced to SFA when the throttle is opened a bit above idle as the manifold vacumn fall then.

    The difficulty is that in the 70s and 80s the pollution controls required meant manufacturers did some stupid things to get old designs over the line with as little change and cost as possible. Some real dogs were made out of good cars. Thank heavens we got past that era. Just do whatever you can to get a solid reliable idle that will work. In years past it was possible to enlarge the progression jets sometimes back to where they were in a previous model to help But the changes need very tiny jet drills,.3-.4mm. I do not suggest this but just mention it as fact.
    Jaahn

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    I wonder whether the fitting is actually a ball bearing check valve. Iím doubtful as if the suck from the engine was intended to close the valve. Then excess fuel would only be able to escape when the engine wasnít running. Doesnít seem right.


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    Thank you for your comments, Jaahn.

    Budge, I also wondered about a ball bearing check valve, but I'm doubtful. When the engine is running, wouldn't any excess fuel be drawn into the engine, simply creating a very rich mixture?

    I'll try the 'very small hole in the end of the tube' approach in the first instance.

    Chris

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    Quote Originally Posted by Budge View Post
    I wonder whether the fitting is actually a ball bearing check valve. I’m doubtful as if the suck from the engine was intended to close the valve. Then excess fuel would only be able to escape when the engine wasn’t running. Doesn’t seem right.


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    Good thought! I was wondering if precisely the same thing was used. It would be similar to the check valve in a 32/34PBIC carb accelerator pump.
    Jaahn, Fuel dumping onto a D exhaust would not be a problem ( other side). Tractions had a long curved drain tube to carry fuel well below the manifold.
    Cheers Gerry

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    Quote Originally Posted by Citquery View Post
    Thank you for your comments, Jaahn.

    Budge, I also wondered about a ball bearing check valve, but I'm doubtful. When the engine is running, wouldn't any excess fuel be drawn into the engine, simply creating a very rich mixture?

    Chris
    Excess fuel would only occur under a flooded situation, IE that created by a failed starting procedure. Once running there would be no fuel excess once any flooding was cleared.
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    Cheers Gerry

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    Quote Originally Posted by gerrypro View Post
    Excess fuel would only occur under a flooded situation, IE that created by a failed starting procedure. Once running there would be no fuel excess once any flooding was cleared.
    Hi gerry
    Actually it also occures in the circumstance when you stop hot and the carby floods and it pools in the manifold, and the fuel pump spring delivers the full shot as well to the carby. The heat helps to keep the fuel boiling in the bowl. Classic situation that the anti pollution methods tried to get rid of. But in this case the fuel will have to be drained to be able to restart or it will be way too rich. You would have to floor the accelerator to clear the excess fuel before it would go at all.
    Just saying. EFI solved a lot of these problems in the end.
    I do not think a ball valve would work as it might clog up with gummy fuel.
    Jaahn

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    Iíve at last had an opportunity to drive my 1974 DS23 BW35 since attending to the inlet manifold drip tube. I fitted a piece of 6mm fuel hose 400mm long to the hose tail installed under the inlet manifold, to which (fuel hose) I fitted a plastic plug at the outer end, drilled to 1.5mm (the smallest drill bit in my tool kit). I fitted a short piece of copper wire in the hole to restrict the 1.5mm opening.

    While I was about it, I removed the breather from the lower nearside crankcase, together with the related pipework. The breather was fairly well clogged Ė and a bit rusty Ė and the hose tail facing the firewall, below the carburettor base on the inlet manifold, was clogged with a solid black material.

    Iím not sure what cleaning the crankcase breather system achieved, but I suspect it couldnít do any harm.

    I then set about readjusting the carburettor. Itís a Weber 28-36 DMA5, which looks much the same as the carby on the right in this video: https://www.youtube.com/watch?v=QYWrzIGJlkI I set the primary and secondary throttle screws so that both throttle plates were barely open at idle and performed the idle adjustment with the mixture adjustment screw (head faces the firewall) and the air adjustment screw (called throttle bypass in the video Ė head faces the air cleaner), using the technique described for the BW35 version in the 814 manual. As my carby has the air adjustment screw, I used this instead of the secondary throttle screw to adjust the idle speed. As noted in the video, given the age of the car, I canít get it to idle reliably at 550 rpm, but starting at about 600 rpm I adjusted the mixture to about half a turn anticlockwise from the stumble point, then finally adjusted the idle speed to about 825 rpm in P.

    During the drive subsequent to performing all of the above work, the car reliably shifted from P or N to R or D and idled Ďhappily?í at traffic lights in D, whereas prior to this each of those actions was accompanied with the ever-present fear of stalling. Only one drive to date, but hopefully it reflects a positive step forward.

    I should add that prior to the above work, the idle mixture screw was set about 21/8 turns off its seat whereas now itís about 3/4 turn off its seat. I assume the former more open fuel passage is reflective of the amount of fuel required to create an acceptable fuel:air ratio due to the additional air then being admitted via the unrestricted fuel drain opening in the bottom of the inlet manifold.
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    Quote Originally Posted by Citquery View Post
    I assume the former more open fuel passage is reflective of the amount of fuel required to create an acceptable fuel:air ratio due to the additional air then being admitted via the unrestricted fuel drain opening in the bottom of the inlet manifold.
    Don't forget that the Citroen design is for an unrestricted drain tube - so it's not really correct to say that, previously, it was getting 'additional' air. 'More' air - yes

    Your modification might well account for the different settings this time around but, as you also adjusted the butterfly settings and cleaned out the oil breather for example, a number of other factors have also changed. BTW, that oil breather pipe has a 'T' piece that leads through a pin hole into the side of the inlet manifold just below the carb.That is easily blocked and needs to be cleaned out.

    Oil breather hose tail: nozzle copy.JPG
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    Thank you for your comment, Budge.

    Some further comments:

    • perhaps I didn't describe my actions in sufficient detail, but I did clear the blockage in the hose tail (whose image you kindly included in your post);
    • my 'take' on the above conversations about the drip tube was that there was some sort of constriction at the outer end; maybe not to the extent that I've gone, but
    • as the Englishman in the video said: 'these cars are now 40 or more years old' (so we need to make some allowances);
    • I adhered to Jaahn's advice (above post): "Just do whatever you can to get a solid reliable idle that will work."; and
    • finally, I forgot to mention that - as per Brian Woodcock's suggestion - I also used a Colortune while adjusting the carburettor.

    Chris

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