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Technical CARBURETOR THROTTLE SHAFT REPAIR

Discussion in 'The Hokey Ass Message Board' started by THE FRENCHTOWN FLYER, Oct 10, 2019.

  1. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    Recently I discovered that my roadster pickup drag car had worn throttle shaft bores. This caused the throttle plates to be loose and leak air into the fuel / air stream. That created an erratic idle that could not be cured by adjusting the idle mixture screws or the curb idle screw. A search on the internet failed to find any good description on how to properly fix the problem. So this article addresses the problem. The carburetors in question are the Autolite 2150 series two barrels. They are a good carburetor with many advantages over other more popular aftermarket brands. Additionally, they are abundant in many bore sizes and available relatively cheaply. The steps outlined in this series apply to other brands of carburetors also. carbush 01.jpg
    The kit I ordered is from HENKYO. It consists of a 7/16” reamer on a 3/8” shaft body. The kit also includes eight knurled bronze bushings. I found it online for about forty bucks.

    carbush 02.jpg
    It was my plan to use the reamer in reverse. That is, insert the 3/8” shaft body into the worn shaft hole to align the reamer and then, by turning the reamer backwards (counter-clockwise) I could ream out the shaft bore on center with the original shaft axis. Well that turned out to be not as easy as hoped for as the reamer would not cut when held backwards and turned in reverse. More on that later…

    carbush 03.jpg
    Placing the carbs on a bench upside down gives access to the throttle plate screws. On these carbs they are #6 screws with extra fine threads. Some brands of carbs peen the threads of these screws; some crimp them; others use trocho-centric (vibration-proof) screws. It may be necessary to grind down the protruding thread with a Dremel tool before removal.

    carbush 04.jpg
    ONE CAVEAT HERE: THE SCREWS HAVE VERY SHORT HEX HEADS. Be very careful not to strip them out! They were tightly secured in the shafts and required that I modify a 3/16” six-point socket by grinding it down to eliminate the slight lead-in chamfer on the socket. Leaving the chamfer in place did not provide enough hex head purchase to loosen the screws (I tried several brands) and the hex will round over before reaching breakaway torque.

    carbush 05.jpg
    carbush 07.jpg

    Mark the location of each plate. Once the throttle plates are removed the throttle shaft is ready to be removed.

    Almost.

    It will be necessary on an Autolite / Motorcraft 2150 carb to disengage the part throttle air metering rod cam from the shaft before the shaft will come all the way out. 2100 Series carbs do not have this feature (often referred to by carb technicians as “crowd control”).

    carbush 06.jpg
     
    Last edited: Oct 10, 2019
  2. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    carbush 08.jpg
    The O.D. of the bronze replacement bushing measures 0.433”.

    carbush 09.jpg
    The O.D. of the throttle shaft measures 0.372”.

    carbush 14.jpg
    The I.D. of the bushing measures 0.375”.

    carbush 27.jpg

    To make the reamer useful for reaming in reverse it is necessary to make a couple of modifications to it. The first and most ticklish mod is to grind needed 45 degree reliefs on the trailing edge (soon to be the leading edge) of the reamer flutes to make it functional to cut in reverse. The second mod is to wrap about four turns of plastic tape around the first half of the reamer flutes. Thankfully, this is a six-fluted reamer so a six point 7/16” socket can be used to drive the reamer in reverse while the tape prevents damage to the cutting flutes.

    carbush 15.jpg

    Now the reamer shaft can be turned around and inserted shaft end first and driven in reverse rotation (CCW) with a slow electric drill so the long shaft will act as a pilot.
     
    Last edited: Oct 10, 2019
  3. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    carbush 17.jpg

    A bushing driver did not come with the kit. Pity. I turned a piloted driver on a lathe so there was no chance of damaging or crushing the bushing during installation.

    carbush 16.jpg

    You are now ready to drive in the bushing. It has a short lead-in area with no splines to make alignment to the bore easy.

    carbush 18.jpg

    carbush 28.jpg

    I use a bushing retaining compound and lightly coat the outer splines with it to secure the bushing in the bore permanently.

    carbush 21.jpg

    carbush 20.jpg


    carbush 19.jpg

    Ream the carb body only deep enough to press in the bushing completely. In the case of this 2150 carb that meant the pilot needed to protrude out past the carb body by the length of the bushing. Ream to required depth. Drive the bushing into the bore.
     
    David Gersic likes this.
  4. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    carbush 22.jpg
    Test fit the bare throttle shaft to insure it turns freely with no binding.

    carbush 25.jpg

    Now comes the re-installation of the throttle plates. Gently stone the edges of the throttle plates on a fine honing stone to remove any factory blemishes. (One of my original plates had a minor burr that had dug into the venturii bore in one spot – hence the need to stone them.)

    carbush 23.jpg

    Apply thread locker to the threads of the throttle plate attaching screws. LIGHTLY assemble the plates in the bores exactly as they were removed, but do not tighten the screws yet.
    carbush 26.jpg

    Back off the curb idle adjustment screws completely before the next step.


    carbush 24.jpg
    Using the plastic handle of a screwdriver gently tap the throttle plates while at the same time applying light pressure to the throttle lever to close the plates and perfectly center them up in the venturii bores. The holes in the throttle plates are intentionally oversized to allow for this perfect alignment adjustment before tightening the screws.
    Make sure everything is squeeky clean and re-assemble.

    After assembly turn curb idle adjustment screws in until they just make contact with the throttle lever. For this multiple carb setup I turned each curb idle adjustment screw an additional one-half turn as a starting point.
     
    Last edited: Oct 10, 2019
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  5. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    There you have it. Two like new throttle bores that are sure to make these vintage carbs perform like new. 303 motor 38.jpg
     
    bct, David Gersic, pitman and 9 others like this.
  6. RidgeRunner
    Joined: Feb 9, 2007
    Posts: 841

    RidgeRunner
    Member
    from Western MA

    Great tech! A true old school, down home, DIY hot rod repair.

    Thanks for your time and effort to put it all together and posting.

    Ed
     
    kidcampbell71 likes this.
  7. dudley32
    Joined: Jan 2, 2008
    Posts: 2,060

    dudley32
    Member

    Thanks for posting...very useful info.
     
    kidcampbell71 likes this.
  8. carbking
    Joined: Dec 20, 2008
    Posts: 2,721

    carbking
    Member

    "Ream the carb body only deep enough to press in the bushing completely. In the case of this 2150 carb that meant the pilot needed to protrude out past the carb body by the length of the bushing. Ream to required depth. Drive the bushing into the bore."

    GREAT article for the DIY'er that does not have the benefit of a good milling machine. Thanks for posting.

    Two of the several really good points you made are: (1) the quotation above which is critical to prevent an internal vacuum leak many experience by drilling all the way through the casting, and (2) the necessity of using a Dremel to remove the upset generally found on the back side of the retaining screws.

    Since I use a milling machine to true the casting, I had never thought of reversing the mill and using the shaft as a pilot - great idea.

    However, I would caution first-timers to buy a junk carburetor at a swap meet for practice. Always best to experiment on something you can throw away ;)

    Jon.
     
  9. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    Thanks Jon.
    Yup, I've got a mill and capabilities to do valve guide Bronzewall inserts in heads too, but I was looking for a simpler way than indicating bores on a mill or burnishing and trimming Bronzewalls. Fortunately the shaft of the reamer was just the right length and diameter to re-do the carb as I envisioned, with a minimum of tools - just a reversible drill and hand tools - available to nearly every hot rodder. Even the piloted driver I made could be approximated by just sliding the bushing over a 3/8" bolt with a shoulder.

    Your idea of practicing on a junk carb is a good one and I have found and bought these Autolite carbs at swap meets for just a few bucks. One of the many reasons I love to use them. Some day I need to do a tech build up on the "how" and "why" of these wonderful, often overlooked carbs.

    Here is the web site for the HENKYO kit. I believe they come in different shaft sizes too.

    https://www.amazon.com/HENKYO-Throttle-Bushing-Repair-Carburetor/dp/B07JZMPFVP

    I have been unable to find a source for additional replacement bushings, even tho the site above shows a pic of piles of them. Any suggestions?
     
    Last edited: Oct 11, 2019
    David Gersic likes this.
  10. uncleandy 65
    Joined: Jan 14, 2013
    Posts: 1,478

    uncleandy 65
    Member

    Great post, Thank for taking the time to walk us thru this..
     
  11. carbking
    Joined: Dec 20, 2008
    Posts: 2,721

    carbking
    Member

    FF - no source for this size.

    Do have a source for:

    ID - 0.375
    OD - 0.444
    Length - 0.5

    Like virtually everything else unusual today, there are minimum quantities required for a decent price.

    Jon.
     
  12. '51 Norm
    Joined: Dec 6, 2010
    Posts: 684

    '51 Norm
    Member
    from colorado

    Great post! I'm glad that you put in all of the little often overlooked steps.
     
  13. Awesome tech article. Thanks.
     
  14. tubman
    Joined: May 16, 2007
    Posts: 4,878

    tubman
    ALLIANCE MEMBER

    I have done this in the past. It was a couple of years ago, but I needed two different sizes and found both with no problems on eBay. It is interesting that you used the reamer "backwards". After looking the situation over, I came to the same conclusion, also using a socket to drive it.

    Great tech.
     
  15. 41rodderz
    Joined: Sep 27, 2010
    Posts: 4,208

    41rodderz
    Member
    from Oregon

    I love tech . I applaud your efforts. Nothing better than a inliner.:cool:
     
  16. I love your articles! Very informative. You are right about these wonderful carburetors. Not everything has to have a four barrel. I love these carbs so much that I wouldn’t hesitate to use them on a gasp! Chevrolet


    Sent from my iPhone using The H.A.M.B. mobile app
     
  17. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    Thanks 51Norm.
    Like most gearhead stuff "The Devil Is In The Details"
     
  18. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,556

    Mr48chev
    ALLIANCE MEMBER

    Thanks for the informative tech article and the well put comments from Carb king.
    I've always like that model of carb as they are just about as simple as anything you can find and easy to rebuild right.
     
  19. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 2,959

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

    LOL
    Full disclosure: I've used the GM Rochester 2GC carbs on my Mustang GT powered tub, since their mounting holes are much more closely spaced together which is useful for tri-power installs. Whatever works best... hottub02.jpg
     
  20. Great DIY article.
    I only had a couple to do, so I bought the inserts off epay. I also bought the long stem reamer there as well. I also could have used my milling machine, but found that it was just as easy to do the job with a drill.
    Bob
     
  21. lippy
    Joined: Sep 27, 2006
    Posts: 4,445

    lippy
    Member
    from Ks

    Very informative and well explained! Thanks! Lippy
     
  22. fullhouse296
    Joined: Jan 30, 2009
    Posts: 382

    fullhouse296
    Member
    from Australia

    Quickfix .Tape up the areas not worn then get a chrome shop to semi bright (Watts) nickel plate for 15 - 20 minutes. remove tape and use valve grinding paste to seat the shaft .clean very well . Works a treat .simple and long lasting !
     
    Truck64 likes this.

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