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Weber Carbs 40 DCNF 101

Discussion in 'Technical Q&A' started by robertgarven, Jul 2, 2010.

  1. robertgarven

    robertgarven F1 Veteran
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    Feb 24, 2002
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    Robert Garven
    Friends,

    I am starting my long awaited carb rebuild on my 75 GT4. I have a few questions for the experts. I have been putting this off for 15 years but now I have two off!

    1. What is the recommendation for grease for bearings and linkage?

    2. Should I use any sealant on the gaskets?

    3. Suggestions for cleaning the carbs and parts?


    Thanks in advance will post some pics

    Rob
     
  2. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
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    1. I am not too picky with this one.
    2. I have not used any sealant on the gasket, due to the nature of the gasoline environment
    3. I used carburetor cleaner (a one gallon bath).
     
  3. flyngti

    flyngti Formula 3

    Jul 16, 2009
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    1. I replaced the bearings so I didn't need to lube them. For the linkage, small dabs of lithium grease on each ball.
    2. I didn't use anything -- gaskets dry.
    3. Ultrasonic parts cleaner with hot water and dish soap. I borrowed one, but Harbor Freight has one for about $60. Ultrasonic cleans everything nicely and the best part is there are no harsh chemicals.
     
  4. BillyD

    BillyD Formula 3
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    Feb 28, 2004
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    Float level measured to float body not soldered seam
    Bearings replaced (superformance UK)removed by homemade Sykes tool no need to remove butterflies
    One carb rebuilt at a time
    Need air balance tool
     
  5. Spitfire

    Spitfire Formula 3

    Nov 16, 2006
    1,546
    Try to avoid soaking in a 1 gallon tin of carb cleaner. I did it this way -- it works, but the stink is unbelievable, and can last for a very very long time (i.e., I spilled some in a plant pot, and three years later, the plant pot still stinks). My wife was very upset with me, and the neighbours even questioned my "environmental spill"!!
     
  6. robertgarven

    robertgarven F1 Veteran
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    I have new bearings but scared to replace them, Billy, do you remember how you removed them I have a draper tool but scared to mess tub the throttle shaft or butterfly?

    !. How do you remove the auxiliary venturis

    How do you remove the choke jets with the washer retaining thing on top???

    I was not planning on re-staking the plugs

    Thanks to all who responded!
     
  7. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
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    chris morse
    Hi Robert,

    Gaskets go on dry, never heard of anyone using any kind of sealant.
    Mike of Pierce Manifold fame strongly recommends installing sealed bearings because it is inevitable that some air will leak past the greased throttle shaft bearings and drive you nuts trying to balance the carbs. It is fussy getting the throttle plates properly reattached but it can be done. Use new screws, grind off the top of the old screws, to be able to get them out. I used a long phillips bit secured in a vise to support the screw head, then used a sharp chisle to "stake" the new screws.
    If you are going to disassemble all of the carbs, pay particular attention to the sequence of the washers and linkage bits, each carb is different. I recommend 4 labled or numbered divided parts bins one for each carb.
    I used Berryman's Chem Tool, air and a small brush. This stuff will eat latex or the usual mechanics gloves and it will really F**K up painted surfaces, like 360 wheel finishes. Use care.
    After pulling the carbs, i suggest also pulling the intake manifolds. First, it will enable you to flatten any surface that is warped. Second, it will enable you to do a valve adjust more easily as well as cleaning off the cam cover gasket surfaces. Third, it will enable you to make sure that the sealing surface on the bottom of the manifold is true. Getting the old gasket off is a major pain but worth it. I also found a ton of corrosion inthe water passages under the intakes.
    Finally, having the intakes off enables you to install 1/8th threaded 90 degree hose barbs, so you can use a manometer, (or rather two 4 cylinder motorcycle manometers) to set the initial carb balance. Your suggestion of adjusting up the throttle cable to take out any slack and get the linkage off of the stops was a great idea.
    Finally, Buy your gaskets from Mike at Pierce and any other bits because his advice is worth a ton, particularly since doing the carbs, (much less getting them off and on) takes so long - a bit of good advice goes a long way.

    htjh,
    chris
     
  8. gerritv

    gerritv Formula 3

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    #8 gerritv, Jul 2, 2010
    Last edited: Jul 2, 2010
    The reason for using carb cleaner is to, guess what, get the carbs clean inside :). Soap and water will not remove years of varnish (from dried out fuel), sand grit and whatever else is in the passages. Cleaning the outside is great but its what is (not) inside that counts.

    Use lots of water and compressed air after letting them soak for >10 hours. Consider removing the lead plugs before soaking, this ensures that you really do get all the passages cleaned out.
    The boost venturis should pull out with some wiggling.

    When undoing the nuts etc on the throttle shaft, ensure that you do not twist the shaft. I.e. do not hold the opposite end of the shaft with a wrench to undo the nuts, use a tool on the flat part of the shaft next to the nut you are removing.
    Grease, you will need something that doesn't turn to liquid at the temparatures found in the engine compartment. Perhaps distributor grease? I use Molykote M77 in many places.

    I use Hylomar (aircraft grade) on most gaskets. Esp. the accelerator pump ones. even after sanding the surfaces flat they will still seep eventually without some help.

    Lastly make sure that the balls on the throttle linkage are truly round. Even a .5mm out of round will drive you nuts trying to balance the carbs.

    Gerrit
    http://dino308gt4.com

    Have you hugged your car today?
     
  9. BillyD

    BillyD Formula 3
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    I was able to get the bearings off the shafts w/out removing the butterflies. I used the same method everyone uses to take the bearings out/off of the camshaft drive gears. Except little bearings are alot easier: drill a hole in bearing cage & and use a screw head ground down on 2 sides, inserted & turned to grab the races & pull with vice grips, about 5 minutes or less per bearing.
    Search the forum & I'm sure you'll find a better description & a Howto
     
  10. Sledge4.2

    Sledge4.2 F1 Rookie
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    when removing the retaining "thing" on top becareful because its spring loaded and if you arent careful, the little bastard will shoot off across your shop floor and you wont be able to find it (ask me how i know). Just gently pry it off with a little screwdriver.

    dont be too intimidated about removing the thottle shaft, not that hard.

    when i reinstalled my bearings, I couldnt get one of the set of plates to close all the way no matter what i did, it turned out my shaft was slightly bent and when i replaced that they easily snapped into place.

    good luck!!!
     
  11. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
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    Rob, before rebuilding, ensure you have matching dcnf's. Plenty of carb'd 308s out there with mismatched dcnfs. It's pretty common for some hack to replace one bad carb with any old dcnf (which inevitably doesn't match) and think the thing is going to run right. Different dcnf's have different progression holes drilled in the bore and this produces materially different A/F ratios, particularly at light throttle.
     
  12. robertgarven

    robertgarven F1 Veteran
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    #12 robertgarven, Jul 3, 2010
    Last edited by a moderator: Sep 7, 2017
    OK Guys,

    Thanks for all your help,

    I cant believe I have gotten this far. I am still scared to continue replacing the bearings with the butterflies in. For you that have done this is there a procedure to do this with the throttle plates in. I am concerned that if I do it wrong I will pinch or dent the throttle plates. I have a sykes tool, but think there might me a correct order to do it in without placing too much pressure on the plates, bearings or shafts.

    I have a matching set and all the jets are stock on this on so far. I have a 45,46,47,48.

    The insides are very clean just the outsides had some varnish where the starter choke cover was weeping. I guess the alcohol in the gas is good for something!
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  13. Ak Jim

    Ak Jim F1 Rookie
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    One of my winter projects is to replace the bearings on my 38DCOEs. Let us know how it goes with out removing the plates.
     
  14. Sledge4.2

    Sledge4.2 F1 Rookie
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    Check the balls on your linkage. Mine were egg shaped, so i drilled them out and replaced them.
     
  15. gerritv

    gerritv Formula 3

    Jun 18, 2001
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    Hi Rob
    Great photo!
    If you keep the throttle closed then the plate is fully in contact with the housing and thus can't move or warp.
    I would avoid removing the butterflies, there are so many other problems to get into while doing that. And you will be left to wonder if you really did stake the new screws properly or not while you are on the track at 7000 RPM :)

    Gerrit
    http://dino308gt4.com

    Have you hugged your car today?
     
  16. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
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    I would avoid pulling the shafts and plates if possible. There have already been several good suggestions for removing the bearings.

    1. If you do not drill out all lead plugs and clean out all passages and verify by passing a probe through them you are wasting your time on the carbs in my opinion.

    2. Never ever use lithium grease on anything. It was a terrific replacement for bear grease in the 18th century. We have progressed. I was tired of removing hardened lith grease years ago back in the old days when I still rebuilt carbs. Its crap. Use something from either the present or previous century.

    3. Do not use sealant of any type on the carbs.

    4. Check the base plates to be sure they are flat. Weber carbs are made of hardened lead and pretty much everyone overtightens everything on and around them.


    5. Buy a fuel injected car. Carburetors are a Victorian age device.
     
  17. robertgarven

    robertgarven F1 Veteran
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    #17 robertgarven, Jul 5, 2010
    Last edited by a moderator: Sep 7, 2017
    Today started out wonderful. I went out and started messing with the bearings on the throttle linkage side on #45 left rear carb. To my amazement after spraying some WD40 on the carb, trying to clean the grease out, I was playing with it and noticed that I could get the inside AND outer races moving so I used a small pair of surgical tweezers and it came right out! I cleaned the area and the Toyo bearings I had got fro my friend C. Jones down under pushed right on

    The bad news is I spent the next 4 hours trying to get the other bearing off! After much pain I finally got it off. The draper blind bearing tool I had was too big and I destroyed two off the attachments trying to make a part that fit. I put some washers on the other side of the shaft and a nut, not to put too much pressure on the plates. The really terrible part is that when I was done I flipped the carb over to notice that when you turn the throttle shaft the bearing turns not on the bearing, but the outside race is moving in the carb! I measured the bearing before I put them in and they exactly the same OD, ID, and thickness. I did not put the other side I had the trouble in yet and am trying to figure out how I can remove the new sealed bearing without destroying it.

    I also would like to get a tool that would help pull the out other ones out so as to avoid so much hardship. I also need to figure out some kind of fix for the slipping bearing. To my credit the ones I took out we almost as loose, so I think spraying the WD40 in the hole, loosened them up (at least the outer race!

    My next problem, I got out the rebuild kits made by WEBCON in the UK and the accelerator pump diaphragm looks really cheap and not at all the same as the one I removed which had a surround like a woofer on it the new piece is just a piece of thin rubber material with a different size round piece on the inside?

    Brian. I wish I had the tools or was smart enough to do the re-staking. The carbs were seeping from the starter cover which had no gasket so that is why I decided to take them apart, also to re-grease, or replace the bearings. If you look at my pick above the insides were as clean as could be. I only put 10K miles on it since the last rebuild and us Chevron with Techron it is, so I pretty sure the passages are all pretty clean the filters were perfect also! The bottom is perfect all the nut and screws on mine were pretty loose.

    Thanks for any help you all can give or have given!

    Rob
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  18. Rifledriver

    Rifledriver Two Time F1 World Champ

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    If you can use a small punch on the bearing seperator and make a space for a couple of small sheet metal screws, you should be able to grab them and remove the bearing. A careful application of Locktite bushing mount will hold the outer race.
     
  19. Sledge4.2

    Sledge4.2 F1 Rookie
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    i removed the lead plugs and apparently didnt clean out all the shavings,etc., as i had to do the job twice. I thought the throttle plates were easy compared to the lead plugs. I tried to get them out cleanly, but apparently didnt. i spend months chasing a poor idle/transition issue, and it turns out i had a clogged idle circuit in one of the carbs (after doing the job twice). anyway, for what its worth if you do restake the plugs make ******* sure the passages are clean as brian notes.
     
  20. robertgarven

    robertgarven F1 Veteran
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    I have successfully reassembled the the carb but have a few more questions.

    1. How tight should the jets be when replaced?

    2. The WSM says two conflicting values for max float height, one is 48mm, which I think is for the Euro cars the other is 50mm.

    I measured the bearings and they matched the original thickness, however after reassembling everything, (I checked twice it seems the accelerator ramp and the throttle control lever on the other side have a small space between them and the carb body. It looks just a little more than on the ones i have not disassembled, the assembly order is correct, the nuts are on tight and the throttle plates have no side play but open smoothly, so i guess I'm OK?

    I will post some pics i even think Brian will be proud of me, I dont know why I was cared all these years and wish i would have done this sooner.

    BTW all jets and parts are spot on original specs! Three more to go
     
  21. CliffBeer

    CliffBeer Formula 3

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    Robert,

    Great to hear things are going well so far. Sounds like you have the right approach (careful and precise disassembly/reassembly). When doing the full rebuild on a set of f-car dcnf's it's not uncommon to find:

    1. mismatched dcnfs (different progression holes drilled in the throats),
    2. stripped or cross-threaded jets,
    3. different/non-uniform jetting across the four carbs,
    4. jets that have been unknowingly drilled out (makes getting uniform AFR just about impossible). Obviously, a jet gauge is helpful here.
    5. heavy sanding and scoring/abrasion marks from rough "cleaning",
    6. poor fitting gaskets and RTV sealant everywhere (plugs up small passageways),
    7. the list goes on.....

    These are all the calling cards of the hack, and make a rebuild to spec very difficult indeed. Wonderful to see you're not running up against any of this type of thing so far. Thanks for sharing the info and pics!
     
  22. robertgarven

    robertgarven F1 Veteran
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    Cliff,

    Thanks for the reply. It seems my carbs were pretty much unmolested till now.

    No one answered my questions and i am hopimg to get some answers so I can get this going.

    I have another more important.

    There is a small ball bearing check valve somewhere in the accelerator pump area. When i disassembled the carb I never saw it and it is not on the exploded parts page, so I am hoping that it is sealed in the carb body behind one of the plug areas. If anyone knows what I am talking about I would appreciate some feedback as I am curious as to whether i lost it and ned to take the diaphragm off again! I have about 4 books on Webers and have been reading them and for some reason I overlooked this part???


    Thanks in advance

    Rob
     
  23. robertgarven

    robertgarven F1 Veteran
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    #23 robertgarven, Jul 13, 2010
    Last edited by a moderator: Sep 7, 2017
    Ok here is where I am at.

    I figured out the ball check valve.

    I noticed that there is more gap on each side of the carb body where the pump cam and the throttle control lever attach to the shaft. I just spent about 3 hours trying to figure out why they have a larger gap than the original and other carbs??? I just measured the bearings and the new bearings are 5.95 mm thick and the original were 5.98mm thick so I know its not that. I am positive I have the parts on the shaft correctly. I apologize for
    damaged threads, this is not like me but this one time I lost control when trying to remove them on the throttle side instead of stoping to think about it I scratched up the threads, mainly the flat part trying to pull the bearing off with a needle nose pliers. I have never seen a shaft but they say they are hollow, well the ends and solid do you think I
    pulled the solid part out of the hollow part? The gap is even on both sides, and the same number of threads are exposed on each side. I did put a nut and washer on the other end while pulling, but I only pulled by hand. I feel like an idiot, and not sure what to do??? The plates have no end play and move freely.

    Should I assemble the others and then measure with a feeler gauge and sand down the spacers to match?????? Should I tap with a hammer on the ends of the shaft????

    Hope someone can make me feel better, I was all excited now very bummed....
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  24. Sledge4.2

    Sledge4.2 F1 Rookie
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    The gap does look a little larger than what I remember...

    IIRC, I couldn't get the cams or the throttle control mech to "seat" all the way on the throttle shaft without tightening the nut to push them firmly into place. Maybe give the nut a few more gentle turns and see if you can visibly watch the cam move inward..

    your other question on jets, I am not an expect but I did hear from a fcar mechanic that if you overtighten the idle jets, you can deform the head making the jet size smaller (i guess by crushing it against the seat), so i have always never cranked any of the jets down when screwing them in
     
  25. robertgarven

    robertgarven F1 Veteran
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    Friends,

    I dont want to do anything stupid so after looking at them for a few hours I think the throttle lever side is ok but my unmolested #47 carb has a .660mm gap on the ramp to body side and the #45 one I cleaned and rebuilt has a .711mm gap in the same place . I was talking to Mike at Pierce Manifolds today and he gave me some good info.

    I have a few other 40 DCNF's, I have collected including one that probably has seen better days. Last night I took off the ramp and took out the small bushing and I am pretty sure I can sand it down with a piece of emery cloth on a flat surface to reach the desire gap. I want the pump cover arm to be in the same place on all of them so they all react similarly. Mike said that this was important which seems logical

    Im not sure what I did as the shaft rotates smoothly, it could be a very small bit bent as when you open the throttle one plate exposes about 1/8 of the first progression hole which is tiny before you see the other one, I think this is splitting hairs even for my OCD condition!. Im sure next week ill be freaking out about something else and this will be forgotten!! HAAA

    Next I am going to do the #47 carb and measure the ramp clearance and see if it still the same after the rebuild. if it is still small .660 like all the other carbs I will sand down that bushing a hair and recheck. I know it is the bushing as the bearing is tapped in place and the cam sits directly on the bushing which sits directly on the the inner race of the bearing. The OEM bearing was 5.98mm wide and the replacement one was 5.95mm, so I cant figure out for the life of me why the gap is larger? I cleaned out the hole very good and tapped the bearing in with a socket from both sides!! What is weird is I counted the same number of threads on both shafts, but thats really not scientific.

    I apologize to all of you and my car for how I scratched up the threads on that side, they look worse in the pic than in real life. I broke my sacred oath not to proceed if I am having difficulties and believe and hope I have not messed anything up that cannot be fixed. I am having a friend make me a bearing puller so I will at least not encounter a similar problem on the other 3 carbs.

    No one answered my question about carb float height, I have conflicting info from data and friends the WSM says 48, others and some Weber books say 50? If any of you have direct experience I would like to hear it!

    Thanks again in advance,

    Rob
     

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