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Technical Using Rochester 2 throat (2GC) with flatty Merc intake

Discussion in 'Traditional Hot Rods' started by jdpaxton, Sep 9, 2020.

  1. jdpaxton
    Joined: Nov 14, 2014
    Posts: 137

    jdpaxton

    Hi. Does anyone know an easy way of operating the throttle lever using the original 1933 firewall throttle lever. The Rochester has the linkage on the driverside and the firewall lever is for pass side Stromberg. I`m thinking a rocker shaft mounted at rear base of carb etc.
     
  2. 51504bat
    Joined: May 22, 2010
    Posts: 2,577

    51504bat
    ALLIANCE MEMBER

    Not sure but I think some just turn the carb around and then the throttle linkage is correct. I'm sure others that have actually used the 2GC on the Merc manifold and they will chime in as to what they did. Also, IIRC the bore on the 2GC is larger than the Merc manifold but it can be machined to match.
     
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  3. Hey @jdpaxton I was running a 4GC on my 283 with the carb reversed using a throttle ball stud on the lower part of the linkage. Worked like a champ. When I swapped the 283 for a 350, I did the same thing with an Edelbrock 1406. The carb just thinks it's going in reverse really fast.
     
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  4. Lost in the Fifties
    Joined: Feb 25, 2010
    Posts: 436

    Lost in the Fifties
    Member

    I'm running a reversed 2GC on a Merc intake on my flathead. It works great! Like bchrismer, I used a ball stud on the carb.
     

  5. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,881

    1oldtimer
    ALLIANCE MEMBER

    I ran one backwards on my '47 with an Offy adapter, worked great. Do you have to open up the intake to run the 2 jet or is it a bolt on and go?.
     
  6. tubman
    Joined: May 16, 2007
    Posts: 5,506

    tubman
    ALLIANCE MEMBER

    I have done this on several engines. The earlier posters are correct in mounting the carbs backwards. It really doesn't care and the fuel line will also end up on the proper side. You have to get one of those bolt on throttle balls that bolt into the 2G throttle lever and take the Ford linkage end. The only problem is the manual choke, as it wants to work backwards. I have ended up using the automatic chokes, as they also are quite compatible. The Mercury's came with both "divorced" (choke mechanism on the manifold) and "integral" (choke mechanism on the carburetor) chokes. Fortunately, GM supplied carburetors the same way, so if you match the carb to the manifold correctly, hooking up the automatic choke is very easy. You simply bend the actuating rod or the choke tube, whichever you are using. The 2G has a 1 7/16" throttle bore, while the Merc manifold is only 1 3/8". I used a 1 7/16" Rota-Broach in my drill press to bore the manifold all the way down and the round the transition with a carbide burr. I have a 1" thick aluminum block that bolts on the manifold and acts as a guide for the Rota-Broach. I have done both aluminum (Canadian) and cast iron manifolds and they cut easily. The hard part is getting the manifold mounted at the right angle in the drill press.

    There are a couple of things to be aware of. First, the bottom of the 2G carburetor has some voids cast into it that can cause vacuum leaks when mounted on the Mercury manifold. Had some 1/4" aluminum adapter plates made to eliminate this problem. PM if you are interested in getting one. Second, while the linkage (at least on a "shoebox" Ford) falls right into place, it will only open the carburetor about 3/4 of the way. While you will still have a reasonable increase in performance, you will not be using the full potential of the carburetor. I have been working on this, but have not come up with a satisfactory solution. My first attempt was to make an extension the bolted to the stock throttle linkage that provided the needed additional throw. However, because of the change in leverage, the car lost a lot of the driveability that it had before. It was so bad that I removed the extension and went back to the "short" stock linkage. I am now working o a progressive unit that will replace the lever on the carburetor throttle shaft with a scroll, that when used with a cable will provide reasonable opening at part throttle, but will open the 2G all the way. Stay tuned.

    Oh yeah, one last thing. You will need a "small base" 2G from the late fifties or early sixties. In the sixties, GM went to the "large base" version that will not bolt to the Merc manifold. They are close, but no cigar. The fact that they are close is also a disadvantage, as the mounting holes are close enough between both versions that a decent adapter is not possible. Believe me, I have tried.
     
    Last edited: Sep 9, 2020
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  7. jdpaxton
    Joined: Nov 14, 2014
    Posts: 137

    jdpaxton

    Thanks to all.
     
  8. 504640
    Joined: Aug 8, 2011
    Posts: 518

    504640
    Member

    That was very comprehensive info, Tubman. It may have saved me a lot of headaches. I have a mostly stock 51 Merc in my '46, which is presently using a 3 bolt carb and manifold. I have the merc manifold and a Rochester 2G on the side. I will have to go inventory what I have and then consider the process!
     
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  9. tubman
    Joined: May 16, 2007
    Posts: 5,506

    tubman
    ALLIANCE MEMBER

    "504640" If need be, I can let you borrow my aluminum guide plate and Rota-Broach if you have a drill press and some skill. (The Rota-Broach is about $40, but it needs an $85 mandrel and I'd hate to lose it.)

    Even with the limited throttle opening, I believe that a 2G on a properly prepared Merc manifold is one of the best upgrades on a street flathead (with a hood).
     
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  10. jdpaxton
    Joined: Nov 14, 2014
    Posts: 137

    jdpaxton

    How about simply buying one of the longer throttle shafts that mount the lever on the passenger side of the carb.? Levers are available to clamp to the new shaft. Then the carb choke can be used with original dash knob. Some 2G rochesters have a fuel inlet on the side and others face front. Lots of good info here guys, thanks
     
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  11. 504640
    Joined: Aug 8, 2011
    Posts: 518

    504640
    Member

    Thanks for the generous offer, Tubman! I'll be PMing you on the project.
    Here is tubman's sweet Rochester set-up that is in his equally sweet 51 ford coupe! Tubmans rochester set-up.JPG
     
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  12. dwollam
    Joined: Oct 22, 2012
    Posts: 1,274

    dwollam
    Member

    @tubman , wouldn't one need a SHORTER arm on the carb to make it open farther? Or a longer arm at the firewall. The rod between the two is traveling the same distance with a short or long carb arm but a shorter carb arm would open the carb farther.

    Dave
     
  13. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,881

    1oldtimer
    ALLIANCE MEMBER

    You need some sort of bell crank set up with the right ratio/angle and somehow make it look good. Maybe an arm built into the carb spacer to hold the bell crank bolt.
     
    1952henry likes this.
  14. 1952henry
    Joined: Jan 8, 2006
    Posts: 806

    1952henry
    Member

    I believe Tubman is steering you straight, but like the idea of a bell crank. Ford used a bell crank in the mid 50s on trucks. 6 cylinder?
     
  15. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,881

    1oldtimer
    ALLIANCE MEMBER

    Truthfully I never looked to see if it was getting full throttle. I put the Ford carb back on the '47. But my bell crank idea was for obtaining full throttle. I like that, an arm cast into the carb spacer holding a bell crank from an old Ford truck, using modified original rods.....might look right at home.
     
  16. Alaska Jim
    Joined: Dec 1, 2012
    Posts: 291

    Alaska Jim
    Member

    If you have a stock carb, and go to the 2gc carb, you will need to change the distributor
     
  17. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,881

    1oldtimer
    ALLIANCE MEMBER

    If you have the Load a matic I think you have too.
     
  18. I used a bellcrank with the 2jet reversed from its normal orientation on my 347 Pontiac engine. Best picture I have on my phone at the moment. IMG_20210202_133811428.jpeg

    Sent from my moto g(8) power using The H.A.M.B. mobile app
     

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