2 stuck Carb Jets during rebuild of DCNF40's - Help Please | FerrariChat
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2 stuck Carb Jets during rebuild of DCNF40's - Help Please

Discussion in 'Technical Q&A' started by tomoshea, Oct 31, 2004.

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  1. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    #1 tomoshea, Oct 31, 2004
    I am in the middle of a complete rebuild on all 4 Weber DCNF40 carbs of my 308.

    No problems with 2 of them but, there are 2 jets that I cannot get out, both are the same jet in different Carbs( low speed right chamber!!) this despite the following.

    The carbs have been soaked in Petrol and oil for 2 days, I have soaked them in Carb cleaner for 24 hours (Xylene based), I have als filled the jet with penetrating with no luck. I have also heated the body up to 150 deg celcius (Hot!)

    I am afraid that if I do any more attempted turning with a screwdriver that I will damage the top of the jet heads too much and never get them out.

    The only thing I can think of is to get a left hand turning self tapping screw (if such a thing exists) turn this into the hole in the jet head and try to use this as a tool to try and break whatever seal thread exists betwen the BRASS AND ALUMINIUM and hopefully (fingers crossed) get the bloody thing to shift!!, however I am nervous of this.

    Anyone have any better suggestions, why is this such a bugger to get out/ other procedures / chemicals that have worked in the past for others?

    Thank you

    Tom
     
  2. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    Philip
    #2 pma1010, Oct 31, 2004
    First, I assume you are referring to the "idle" or low speed jet. It is held in place by a retainer, made, I believe, from brass, a soft metal, which has a slotted head. Also, the Webers are made from a "funny" alloy, that if you bugger it up, can't be welded.

    You've done all the things I'd usually do -- PB Blaster or similar. If you believe you are at the point of no return, then I think you have to drill with an "easyout". Remember though, the body of the retainer is hollow.

    Sure you can't put a driver bit into a socket and turn it out?
    Good luck.
     
  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Russ Turner
    #3 snj5, Oct 31, 2004
    Tom
    I truly understand your frustration. I am not very sure just which jet you are talking about yet. If it is a replacable brass jet, would just worry about not damaging the soft metal carb body - all of the brass pieces can be replaced.

    The acknowledged experts on this are the Pierce Manifold (www,piercemanifolds.com) folks who are very helpful. Due to the rare irreplacability of the uniquely Ferrari '5-screw' 40 DCNF bodies, I'd be tempted to send them in to Pierce and let the pros work this one.

    I know this is not a magic bullet answer, but would sure step back from it, have a beer and call Pierce....

    Best, and Good Luck!
    Russ

     
  4. Martin308GTB

    Martin308GTB F1 Rookie

    Jan 22, 2003
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    Martin N.
    #4 Martin308GTB, Oct 31, 2004
    Tom, sorry no 100% solution at the moment, but avoid any attempts with self tapping left hand threaded screws or similar. These and any tools which work with this principle expand the screw - or like in your case, the jet - and the chance is big, that this makes things worse.

    Best Regards

    Martin
     
  5. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
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    Tom O'Shea
    #5 tomoshea, Oct 31, 2004
    Guys Thanks,

    to be clear which jets I am talking about. Looking at the Carb from the top, the float well is at the back, the 2 main jets are right beside each other justin front of the float well.

    The Idle jets are on the side of the carb body in line approximately with the main jets. normal brass screw heads on both of these. these are not a problem they come out easy and have a rubber gasket seal on them.

    Now moving to the far side of the venturis, towards the front of the carbs there are two smaller jets (Hollow brass which I believe - though I may be wrong are - up to about 300O RPM ? these are down in the body of the carburettor).

    These are the buggers that won't come out, only the right side jet on both carburettors

    Air flow appears to be OK through them no blockages apparant so maybe it might be easier to leave them in place and just rebuild as is?

    I presume there are replacmeents available for these jets?
     
  6. don_xvi

    don_xvi F1 Rookie

    Nov 1, 2003
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    Don the 16th
    #6 don_xvi, Oct 31, 2004
    You're describing the air correctors. They're actually used for high speed operation. They meter air only, not fuel. Heck, I'd leave em be!
     
  7. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
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    Tom O'Shea
    #7 tomoshea, Oct 31, 2004

    Do you mean that these are used for balanceing flows between the two venturis, via the bypass valves?

    To be sure we are talking about the same thing I have attached a powerpoint slide of where exactly the problem is.

    The jet I am talking about links back to the bottom of the float chamber and the 2 small holes to its right (shown as black solid circles in the drawing).

    Can I really leave the alone ?
     
  8. pma1010

    pma1010 F1 Rookie

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    #8 pma1010, Oct 31, 2004
    No, the air correctors are at the back, near the floats. I think he's describing either (i) the starter jets ("choke" or cold start enrichment). If so, these have a small circlip around the top which can be pried out and the body of the choke jet can be persuaded to come out by removing the choke actuating cover; or, (ii) you are describing the air balance screws. These have a small hex nut on them which is wound out and then the rest comes out with a screw driver.

    Either way, look at the Pierce site, open the DCNF pic and tell us where you are stuck!
     
  9. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
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    Tom O'Shea
    #9 tomoshea, Oct 31, 2004

    Guys I am referring to part number 63 on Piercemanifolds site, it is listed as the STARTER JET - this is what is locked solid.

    Philip what you are referring to is part 64 and associated bits called the starter valve piston - This is not a problem for me working fine, does not need to come out.

    Hope this helps with suggestions ?
     
  10. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    #10 snj5, Oct 31, 2004
    Hmmm

    Nobody ever uses the starter circuit (a.k.a. 'start enrichment' d.b.a. 'choke') that I know of. Would be tempted to leave it alone unless you have a need. Just a couple of quick hits on the accel pump is usually all required.
     
  11. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
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    Mitchell Le
    #11 yelcab, Oct 31, 2004
    A picture is worth a thousand words. Please post one.
     
  12. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    #12 pma1010, Oct 31, 2004
    63 and 64 are all part of the starter jet. If you are desperate (why?) to pull it out, I think you've identified the path. Most of us don't use this circuit, there are too many possibilities for the "chokes" not returning to "off" and leaving you with an enriched mixture.
    Philip
     
  13. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
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    Tom O'Shea
    #13 tomoshea, Nov 1, 2004
    OK Guys,

    I never use the choke either, if this jet is only associated with the choke I will leave it be and not take it out.

    Are you saying that it has no impact other than the choke function ? i.e. it won't impact me on acceleration or cause any backfiring etc if it is not clean?

    If this is the case I won't take it out, too much hastle.

    Can anyone confirm this is correct?
     

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