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complete 308 carburettor strip down and overhaul question

Discussion in 'Technical Q&A' started by Martin308GTB, Dec 20, 2011.

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  1. Martin308GTB

    Martin308GTB F1 Rookie

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    #1 Martin308GTB, Dec 20, 2011
    Hello from Germany,

    recently I purchased a complete set of 40 DCNF 57 - 60 carburettors ( exactly the same series like those on my car ) and would like to rebuild them completely.
    After a carburettor overhaul some years ago I have a little bit of experience but not regarding a really complete strip down.
    Therefore my question before damaging something;
    what is the best way to remove the auxiliary venturis and afterwards the venturis ? They are stuck. From what I see on the manual illustrations the auxiliary venturis are just held in place with the help of a spring mechanicsm. But I cannot get them out with my hands and want to avoid applying any inappropriate force with crude tools.

    Best Regards and thank you in advance

    Martin
     
  2. Sledge4.2

    Sledge4.2 F1 Rookie

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    #2 Sledge4.2, Dec 20, 2011
    just a little gentle coaxing. The aux venturi has a spring loaded circlip, wiggle the venturi (gently) from side to side and just pull i out (assuming the top of the carb is off :) ).

    The main venturi also just pops out as well...maybe try some penetrating oil to loosen it up?

    Are you restaking the lead plugs?
     
  3. Sledge4.2

    Sledge4.2 F1 Rookie

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    #3 Sledge4.2, Dec 20, 2011
    Last edited by a moderator: Sep 7, 2017
    Martin, I just pulled a spare carb body and pulled the venturis:

    the aux venturi is held in by a spring clip (which is oriented towards the choke). Wiggle back and forth with some pentrating fluid.
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  4. Sledge4.2

    Sledge4.2 F1 Rookie

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    #4 Sledge4.2, Dec 20, 2011
    the main venuturi on my spare throttle body is "spoiled" in place" with punch marks, a pair on the venturi, and a pair on the carb body. The venturi should slide up to the top of the carb body without too much effort. To get it out, you need to file away enough of the spoiled metal (not too much) and it slides out. However, there is no reason i can see to pull that venturi, as you can clean the carb body passages by just sliding it to the upper position.

    Geno
     
  5. Sledge4.2

    Sledge4.2 F1 Rookie

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    #5 Sledge4.2, Dec 20, 2011
    Last edited by a moderator: Sep 7, 2017
  6. FasterIsBetter

    FasterIsBetter F1 Veteran

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    #6 FasterIsBetter, Dec 20, 2011
    If you don't have it, pick up the Weber carb book by Pat Braden that is available from various sources, including places like Amazon. It's not expensive, and tells you just about everything you need to know on overhauling them, jetting them, tuning them, etc. Takes the guesswork out of the process.
     
  7. Martin308GTB

    Martin308GTB F1 Rookie

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    #7 Martin308GTB, Dec 20, 2011
    thanks a lot so far. Especially Geno for the effort of taking pictures.
    I will try it tomorrow. This evening I have soaked them with penetrating oil. And yes, I will restake the lead plugs but will not remove them.
    I have described the procedure for this some years ago here on FChat. Have to find it, but it's late now over here :)

    The Braden book on carburettors I have since many years. But there is not much DCNF specific stuff in it. I found it very useful for the overhaul of my Alfa DCOE carburettors.

    Best Regards

    Martin
     
  8. Sledge4.2

    Sledge4.2 F1 Rookie

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    #8 Sledge4.2, Dec 20, 2011
    I would be interested in see in the "restake but not remove" option for the lead plugs. I assume you just repunch the lead stakes, and they further expand to stop the weeping...
     
  9. swift53

    swift53 F1 Veteran
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    #9 swift53, Dec 20, 2011
    If the lead stakes are there, I would remove and clean what's behind that dead end...

    Regards, Alberto
     
  10. Sledge4.2

    Sledge4.2 F1 Rookie

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    #10 Sledge4.2, Dec 20, 2011
    I've done that, but was curious as to the OP'ers idea of restaking without removing the plugs
     
  11. Peter

    Peter F1 Veteran
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    #11 Peter, Dec 20, 2011
    Martin, you should get in contact with Rob Garven here on F'Chat as he rebuilt his set last year during his major rebuild.
     
  12. Martin308GTB

    Martin308GTB F1 Rookie

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    #12 Martin308GTB, Dec 21, 2011
    Peter, I have read Rob's postings about the carburettor rebuild.
    There are indeed some useful hints.
    But this time I will remove the butterflies and throttle shafts.

    Best Regards

    Martin
     
  13. Martin308GTB

    Martin308GTB F1 Rookie

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    #13 Martin308GTB, Dec 21, 2011
    Last edited: Dec 21, 2011
    this was my write-up from 7 years ago. Since I will ultrasonic clean the housings it's mandatory to restake the plugs.
    So far I don't know whether I should go the hard way of removal of the lead plugs.
    Two Weber specialists advised against it.

    http://www.ferrarichat.com/forum/showthread.php?t=35524

    I have a heated ultrasonic cleaner and tried the first housing yesterday just with water and dishwashing detergent. The result is convincing.
    I have ordered a special ultrasonic cleaning fluid for carburettors and will have to see what happens with this.


    Best Regards

    Martin
     
  14. swift53

    swift53 F1 Veteran
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    #14 swift53, Dec 21, 2011
    Martin, I think the ultrasonic cleaner is the way to go. What brand/model is yours?
    Checked on Amazon and found one that can even fit DCOE's, even though they probably have to flipped a few times...
    On another note, what is the issue about restaking the plugs? I still think they have to be removed to clean out passages properly and squirt some air through to really be thorough.

    Regards, Alberto
     
  15. gcmerak

    gcmerak Formula 3

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    #15 gcmerak, Dec 21, 2011
    Hi Martin,

    If you are going to take out the the throttle plates/throttle shaft for the purpose of putting in sealed bearings, you will need to chase the threads [usually one side] of those screws to back them out. Make sure U use a hollow ground screw driver on those heads.

    Ciao,
    George
     
  16. Peter

    Peter F1 Veteran
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    #16 Peter, Dec 22, 2011
    Are you sure about that? I've always avoided this as that is a very tedious process. Rob experienced that and was stuck so bad that I even made him a custom extraction tool for the bearings...
     
  17. Martin308GTB

    Martin308GTB F1 Rookie

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    #17 Martin308GTB, Dec 22, 2011
    Last edited: Dec 22, 2011
    Peter; already done one one carburettor. I will post pictures during the christmas days.
    I had no problem undoing the screws and removing the butterflies and shaft. I grinded off the caulked screw ends, cleaned the shaft and checked that there are no burrs around the threads in the shaft. Then they came out without any problems. Just slighty tapping with a piece of hard wood.

    @Sledge4.2; thanks a lot for your hints regarding the venturis. I have removed the aux and main venturis as well. But the 'spoiled metal' did not only hold the main venturis in place, but also the aux venturis. I had to remove a tiny bit material around those punch marks and venturis came out.

    Best Regards

    Martin
     
  18. Martin308GTB

    Martin308GTB F1 Rookie

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    #18 Martin308GTB, Dec 22, 2011
    Alberto, my ultrasonic cleaner is something like this:
    http://www.ebay.com/itm/Pro-5-5-Liters-450-W-ULTRASONIC-CLEANER-LAB-DENTAL-Cleaning-w-Heater-ef6-/140663201406?pt=LH_DefaultDomain_0&hash=item20c02e1e7e

    It takes a complete DCNF using the basket and a full DCOE without the basket.

    Did you ever perform removal and refitting of all thirtysomething lead plugs on each carburettor ?

    Best Regards

    Martin
     
  19. Sledge4.2

    Sledge4.2 F1 Rookie

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    #19 Sledge4.2, Dec 22, 2011
    I removed and restaked all the lead plugs and pulled the throttle shafts when I redid the bearings.

    On the lead plugs, if i had it to do over again I probably would "repunch" them per your earlier posting, and see if that stopped the weeping. In the process of restaking them, it turns out I got a little bit of lead shaving lodged in the low-speed circuit, and it took me months to figure out why I couldnt get one cylinder to fire right at low speed. Turns out the shaving was blocking the passage. I dont konw the best way to remove the plugs, I took a small drill bit, sunk it into the plub, and tried to jerk them out. Some came out cleanly, others i had to ream out.

    On the throttle shafts, the key is the be very careful withe the shaft as it bends easily, and one slight bend and those plates will never seat correctly. The spoiled screws on the throttle shaft means you have to put some pressure on the shaft to free up the screws, and therein lies the risk of bending the shaft. Turns out I bent one, and had to get another shaft as i couldnt get the plates to seat perfectly. If you dont mess up the shaft removing the throttle plates, its just time and patience to get the realigned (set screws semi-loose and snap the shaft open and shut), and set with new screws. I personally wouldnt re-punch the throttle plate screws at the risk of bending the shaft, but rather compress them with a pair of channel locks....
     
  20. swift53

    swift53 F1 Veteran
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    #20 swift53, Dec 22, 2011
    No Martin, never have removed and restaked the lead plugs, thus my curiosity.
    Is the ultrasonic wash sufficient?

    Regards, Alberto
     
  21. Martin308GTB

    Martin308GTB F1 Rookie

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    #21 Martin308GTB, Dec 22, 2011
    Alberto; I do not know, whether the ultrasonic wash is sufficient, but the first housing I tried with the special cleaning fluid I got yesterday, is incredibly clean.

    I just don't want to open this particular can of worms with removal of the plugs. And this is the exact terminology both Weber specialists I talked to, used - one of them an old retired guy, who worked for decades on these carburettors.
    Geno; your example with the plugged idle circuit is ONE thing which can happen. The other things we even don't know yet :)

    Best Regards

    Martin
     
  22. Martin308GTB

    Martin308GTB F1 Rookie

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    #22 Martin308GTB, Dec 26, 2011
    Last edited by a moderator: Sep 7, 2017
    Hello all,

    o.k.; during the last few days I was busy with dismantling and cleaning the carb housings. All parts came off without problems. Just one single venturi needed the help of a special tool I had to fabricate on my lathe. Just a plastic punch diameter 40mm- and slight hammering. I think, soaking in WD-40 for some days helped significantly. So nothing went wrong so far, but I have a question:
    While ultrasonic cleaning I recognized, that I need several cleaning cycles, because some kind of chalk like residue was very stubborn. I got rid of all kind of carburettor typical dirt, but on several spots the above mentioned residue remained. Only repeated cleaning removed it.
    I used a mild carburettor ultrasonic cleaning stuff especially made for sensitive classic cars zinc diecast carbs.
    My question; does anyone of you know definitely; whether the DCNFs on the 308 cars are made from zinc diecast or aluminium diecast ?
    If the latter applies; I could use a stronger cleaner which contains citric acid.
    The one I have is alkaline, free of any acid. It's more gentle, but the aluminium cleaner is more aggressive.

    One of the pictures shows one carb in original condition and the other shows the one housing which is already bead blasted.

    Best Regards from Germany

    Martin
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  23. yelcab

    yelcab F1 World Champ
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    #23 yelcab, Dec 26, 2011
    bead blasting carburetor? I would hate to find all the places where the little beads could end up. You will be hard pressed to get them all.
     
  24. Martin308GTB

    Martin308GTB F1 Rookie

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    #24 Martin308GTB, Dec 26, 2011
    all carburettor workshops over here do it. Repeated flushing is important.

    Best Regards from Germany

    Martin
     
  25. Martin308GTB

    Martin308GTB F1 Rookie

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    #25 Martin308GTB, Dec 26, 2011
    and I forgot to mention, that I plugged or covered all holes prior to blasting. To minimize the amount of beads entering the internals.
    For example I covered the progression holes with tape. Taped the whole base, made a 'top cover gasket without the venturi bores', installed the pump cover together with a used diaphragm, etc. etc.
    Nevertheless thorough flushing is inevitable.

    Best Regards

    Martin
     
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