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Opinions sought on carby rebuild

Discussion in 'Technical Q&A' started by kerrari, Jun 23, 2005.

  1. kerrari

    kerrari F1 World Champ
    Silver Subscribed

    Oct 22, 2004
    16,205
    Coolum Beach, AUSTRALIA
    Full Name:
    Karen H.
    I have been contemplating having the carbies on my 1980 308GTS (HK delivered so assume Euro spec) rebuilt mainly because one refuses to play nicely with the other 3 ie mechanic and carb specialist don't seem to be able to get it balanced. The manifestation is this one runs rich and therefore pops & backfires when backed off at street speeds (not generally at highway speed). Note car does not have the backfire at switchoff problem.

    Car starts, runs and pulls cleanly through the rev range, plugs are clean, and economy is around 13l/100km. Car is run at least weekly for a minimum of an hour, usually at highway speed. Also occasional motorkhana and trackwork (at 'fun' not 'serious' speeds).

    My main concern is if constantly running rich, the affected cylinders might get washed down and hence be short of lubrication. However, I'm now getting cold feet about messing with something that may be better left as is.

    Any comments? I've been downloading all the threads from here regarding jetting, float level etc but just wonder what the general consensus on this is - rebuild or live with? Also, do all four need to be done or just the problematic one (assuming same size jets went back in)?

    Thanks in anticipation, K
     
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  3. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
    8,520
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    Phil Hughes
    I've never found one yet that can't be made to play ball with the others, but that said, to make them really nice, you should rebuild them all as a group.

    The shaft bearings are open as std, and sealed bearings make them much better and longer lasting. Gasket kits are a little pricey but readily available, any obscure parts required through damage or abuse will be tricky to get.

    It's no big deal though........ Full carb rebuild, tune and synchronise is about 24 hours work. Any underlying ignition or valve train faults can often cause mis diagnosis though, so maybe just give the car a major service at the same time to start with a clean slate and not waste investigative labour that a service would fix as a matter of procedure.

    A full carb rebuild done at the same time as a full service, would only add about 12 hours to the whole service job.
     
  4. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    Rebuild is easy, no special tools required, just patience, every part for the carb required can be sourced. Nothing too expensive - use superformance in the UK or Pierce in the US.

    My rebuild kit cost me £ 50 stg and I also replaced the bearings on all 4 at about £16 stg.

    the main time consumer is getting them off and on the engine there is a sequence for on and off!! - rebuild is about 1 hr a carb. Thought most people take the time to really celan the exterior which can take a lot longer.

    I am not a professional mechanic, so I think anyone with a bit of patience can do it.

    There is a great thread on the site on rebuild procedure and how to synch the carbs. Did this myself also no problem, just takes time.

    If you go down the rebuild route, don't waste your time with the choke jets or mechanism - it is never used on a Ferrari.

    Best of luck.

    My engine drives like a dream since the rebuild no pops, backfires or dead spots.
     
  5. docweed

    docweed Formula Junior

    Dec 8, 2004
    452
    Morgantown,WV
    Full Name:
    Chuck Stewart
    I'm curious about your rebuilds ...did you have difficulty removing the retaining screws that hold the throttle valves. Did you have any trouble getting them out? I think mine were peened at the factory and I don't want to harm the screws or shaft. Any advise?
     
  6. Peter

    Peter F1 Veteran
    Rossa Subscribed Owner

    Dec 21, 2000
    6,403
    B.C., Canada
    Don't touch them! Leave them be. You can re-build the carbs without having to touch them... Unless of course, they're buggered-up to begin with.

    Remove the chokes, hold the carb up to a light and look for an even pattern of light around the throttle plate. If it's even, then leave them in there.

    If not, yes, you'll have to grind the staking off the ends of the screws and re-set the plates (do so by leaving them on the shafts, snap the throttle open and closed a couple of times and check for position using the above method I mentioned). When satisfied with the plate position re-stake the new screws by carefully and robustly supporting the shaft and hit the end of the screw with a small chisel and hammer. Don't swing on the hammer like an ape, just a gentle tap to deform the end of the screw thread.

    It's a sensitive procedure. Practice on an old used motorcycle carb before doing the Ferrari's.

    I've used the rebuild kits supplied by Superformance in the UK. No problems.
     
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  8. docweed

    docweed Formula Junior

    Dec 8, 2004
    452
    Morgantown,WV
    Full Name:
    Chuck Stewart

    Thanks Peter
    I agree with about leaving the throttle plated alone except I am thinking about replacing the bearings with the sealed type. They are not cheap ($27 to $36 ea.) but it makes some sense that air could eventually start leaking around and thru them with time...I don't know. What do you think Pete is it worth the time and expense? Also if I may ask another question...what is the correct gasket that goes between the carb base and the manifold? The one I took off the carb is about 5mm thick. The replacement gasket is only about 2 mm. The gasket i took off has copper "spacers" in each of the bolt holes and it appears to have two thin gaskets...one on each side of the thicker gasket. I read somewhere that it may be an insulator of somekind. If that is the case would I not save it? Should it have a thin gasket on both sides? What is the 2mm gasket for that they sent me? Thanks for your help.
     
  9. Peter

    Peter F1 Veteran
    Rossa Subscribed Owner

    Dec 21, 2000
    6,403
    B.C., Canada
    I experienced those air leaks around the bearings and shafts and it made the car drive like crap. Sealed bearings would help. I got around that by just using a heavy bearing grease and inserted home-made teflon washers between the carb body and the throttle shaft attachments to seal it up further. After that, no running problems.

    I have a hard time believing those bearings would be $36 each. Visit a local industrial bearing supplier and I'm sure you'd be able to get those for much less.

    The original 5mm is the correct gasket. Save it if the paper gaskets on either side of it are in good shape. Don't know why your kit came with 2mm gaskets. Although the Superformance kits don't come with these 5mm insulator gaskets and I think during my last order with F of UK, they list them, but were out-of-stock at that time. My originals are always in good shape, so I re-use them.
     
  10. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
    8,520
    Melbourne
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    Phil Hughes
    I disagree about the butterfly screws.

    They can be tricky to remove, but so long as your screwdriver fits perfectly and you keep firm pressure on them, they'll come out.

    Just turn them and the peened area will smooth itself over. Refit them after with loctite and don't peen them.

    Leaving them in is acceptable, but not a thorough job. The butterflies can be twisted or damaged or just very dirty or not set correctly. Changing the bearings is complicated with the shaft in situ, and packing them with grease will not last very long... the fuel will just wash it out over a period of time.

    The sealed shaft bearings are availabe from various sources but try carl888 on ebay for starters!
     
  11. Martin308GTB

    Martin308GTB F1 Rookie

    Jan 22, 2003
    4,125
    Black Forest Germany
    Full Name:
    Martin N.
    Hello,

    removing the screws withoug grinding the screw ends can be risky. Eventually they come out but it's possible - not necessarily but possible - to damage the thread inside the throttle shafts beyond repair.

    Best Regards from Germany

    Martin
     
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  13. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Hey Phil:
    Not intended to bust your chops or derail the thread -- I think many good points have been made here. FYI, hourly rates in authorised US Ferrari dealers have risen 4 years ago from $90/hr to $140/hr. 24 hours to R&R carbs is $2400 plus parts. At that price, a "DIY" effort is worth doing. A 30K service is budgeted at my local dealer as $7500 (US) (includes WP, changing various hoses etc). Silly money.
    Philip
     
  14. docweed

    docweed Formula Junior

    Dec 8, 2004
    452
    Morgantown,WV
    Full Name:
    Chuck Stewart
    Hey guys
    Thanks for your help and advise I surely appreciate it. A brief up date in my struggles to make my car purr. I ordered some new throttle retaining screws from Pierce Manifolds so I'm going to carefully grind the peened areas from the old screws. I'd like to say that Pierce Manifolds is a top notch place to deal with and they are really helpful. A great place and a guy named Steve is number one. Like to give credit when and where it's due.

    When I did get the bearings out I was going to go to a bearing place to see if they could match the old ones but Carl Jones (Carl888 i think) told me that he had already shipped a set of the sealed bearings today and if I liked them I could trade something for them. Great guy don't you think? I had talked to him after I missed a set he had on ebay. Nice guys own Ferraris!

    I've owned my 308 for 4-5 months and have had it torn apart most of the time working on it and learning what makes it tick. I'm having fun though and that what toys are for...right. AT $140 and hour for a F tech I'll DIM (do it myself). Thanks guys and as my Grandmother would say, "Your peachy keen".
     
  15. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Phil Hughes
    Hi Philip, yeah, absolutely understand your point. If you're game for it have a go... but beware the pitfalls, that's all.

    I'm doing 2 308 carb cars at the moment, one a fire damaged car, and I'm getting all the steel linksages/parts re plated etc too. It's going to be more like 35 hours per carb set... but at Aussie rates it's bareable. Still pricey though.

    FYI, I offer customers the chance to work on their own cars in the shop on occasion. This month a BB owner had a ball and learned heaps while saving himself money!!

    Yeah, and I share a shop with Carl... we try to be nice, to those that deserve it anyway!!
     
  16. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    I have done a complete rebuild.

    If you are going to rebuild do it properly, replace the bearings or at least take the covers off and fill the bearings with grease of some sort to prevent / minimise potential for air leaks.

    For what it takes it is worth the effort.

    if you are going to remove the butterfly plates it too is easy, you just need the right sized screwdriver - they are stiff! (and note which side of the shaft the heads screw into/ they will not go in the other side without damaging threads badly!!),

    Also mark the butterflies as they can get mixed up and wear patterns will not be the same on each of them, note which carb you have removed them from and which venturi. Replacements can be purchased not too pricey.

    Finally make sure that you put thread lock on the butterfly valve screws when you do refit them. (Don't want one inadvertently falling into a cylinder!!)

    Take your time, write notes and it is an easy job, as is setting the float height in the carbs
     
  17. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    10,525
    San Carlos, CA
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    Mitchell Le
    I would not touch the butterfly unless you absolutely have to.
     
  18. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    The butterfly screws are not the most treacherous things to do come across when overhauling carbs.

    Most common problems are overtightening the nuts when installing... warping the base, and the other one easy to do is to twist the spindle shaft when tending to the nuts on each end.

    In fact almost all pit falls come from overtightening, the reverse of this is when using fibre washers on the banjos and plug... these need to be tight, or better still... get rid of them and use copper/alloy washers
     
  19. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Phil
    FYI: I have not had a problem with fibre on the banjo fittings (and they've been off and on many times). I have found it important to use the Weber ones. Anything else seems to leak all over the place.

    I second the point on not taking off the plates unless absolutely necessary. Too easy to b***** it up.
    Philip
     

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