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Warped carburetor tops

Discussion in 'Technical Q&A' started by Dandy_Don, Apr 2, 2004.

  1. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    79 308GTS Just noticed that 2 of my 4 DCNF carburetors have warped tops. One is very badly warped, one side seals to the body therby causing the other side to lift perhaps 1/6" to 1/8" off the body. I have searched the old archives of both forums and found nothing. Am I the only one to have encountered this? Would Pierce Manifolds carry and sell replacement tops for the carbs. Thanx all Don
     
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  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,282
    Texas
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    Steve Magnusson
    (Maybe unfortunately) the carb tops on the F version of the DCNF are a sort of special 5-bolt style -- IME Pierce, SuperformanceUK, etc. only have the 4-bolt top cover DCNF style available (but wouldn't hurt to give them a shout about the 5-bolt style). Sorry to only give bad news -- good hunting/repair...
     
  4. henryk

    henryk Formula Junior

    Dec 9, 2003
    479
    Door County, WI
    How about machining the top "flat", and adding a brass spacer........of the correct thickness, to compesate for the height.

    I don't know if this is possible........just a thought!
     
  5. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    I don't believe Pierce (or anyone else) sells the tops (or the bodies for that matter). It is strange to me that they have warped that much. I'd guess you'd be able to get them leveled by a good machine shop, but otherwise, I think you are going to need to bite the bullet and find another set/couple of carbs of matching series numbers (so the progression holes are equal across the group). You might ask Mike (at Pierce) if he can level them.

    If you do get them leveled, check the float alignment when you rebuild - you don't want it to stick, leave the needle open and hydralock the motor...

    Good luck.
     
  6. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    Warping is VERY common on these carbs - as well as other brands.

    A zillion years ago, a top carburetion specialist showed me how he uses a very large flat file and goes over all the carb surfaces. I did this with my Webers.

    Most of the warpage seems to be on the carb body itself. Virtually all choke covers leak because of high spots in the surface that the cover bolts to. My carb tops were straight, but there were some serious high spots in the carb body itself. One carb had a big lump where the venturies were staked into place, causing the cover to 'rock' by nearly 1/8". It has apparently been this way for nearly 30 years.

    If you file any of the surfaces, you'll need to do a major cleaning (ie - disassembly) to remove any filings.
     
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  8. Smiles

    Smiles Moderator
    Moderator Owner

    Nov 20, 2003
    14,109
    Pittsburgh, PA
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    Matt F
    You can also put some emery cloth on a largish piece of glass and grind it flat.

    (By the way, what's a SIXTH of an inch?)
     
  9. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    Yeah, emery cloth on glass is a good idea. However, it would have taken too long to remove the large amount of metal that I had to. Also, you can't do the tops that way because the pedestal that the float hangs from is in the way.

    Some cringe at the idea of using a file. But if you take it slowly, keep switching directions, and observe what's going on, it WILL give you a very flat and true surface. Check it with a straight edge and thin feeler gauge, if you wish. You can readily see what areas metal is being removed from. Part of the secret is to get a seriously LARGE file. For example, on my carb tops, a quick, light pass with the file revealed that the entire surface was being contacted by the file. Therefore, they were true and didn't need further tinkering with. The bodies on the other hand........
     
  10. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Well, Once again I have gotten some great advice from this board. 4e GT4, you had it nailed. Instead of a large file which would work I tried a piece of bar stock (about 2" wide) and wrapped it with emery cloth. I then used the sand a little, check, sand a little process described below-probably spent an hour on this top but it was very bad. It actually is not that hard to get a flat surface. I had gaps in one place of 1/16" to 3/32" before starting and now when screwing the 5 screws in I can no daylight all the way around without using a gasket. If you are rebuilding your carburetors this is probably something that you should check and fix if you detect any warping. I was lucky in that all of the carb bodies were straight and it was only 2 tops that I had problem with. With the worst one now fixed I will tackle the marginal one. Again thanx for the advice. Don
     
  11. Dave

    Dave F1 Rookie

    Apr 15, 2001
    2,722
    Little Rock
    Full Name:
    David Jones
    Be sure to sand in a figure-8 on a large flat surface.
     
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  13. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Dave, as 4re gt4 points out you actually can't sand the carb tops on a flat surface in a figure 8 pattern as the cast supports for the float prevent one from doing this. The figure 8 pattern would be possible (and advisable) for the top of the carb body or the mating flange to the manifold but not possible on the carb top. For that it is the slow method described earlier. No hand held grinders either, but since the carb material (aluminum it looks like ) is soft this is not really a long process. Just take it slow and check often. Don
     

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