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Technical Rochester BC choke vacuum question

Discussion in 'The Hokey Ass Message Board' started by 1pickup, May 7, 2018.

  1. 1pickup
    Joined: Feb 20, 2011
    Posts: 881

    1pickup
    Member

    Got 2 matching (almost- a '59 & a '62) Rochester BC carbs on my 250 in my wagon. Rebuilt them. Got some vacuum pulling from the chokes (stove tubes?) Did a search & found conflicting answers (of course). So, what's the course of action here? Plug them & forget about it? Hook up some sort of stove tube to the manifold? It's an Offy intake & I don't see where that can be done. Other suggestions? It seems to idle smoother when I put my finger over the holes. Doesn't seem to have much effect on the road. Thanks.
     
  2. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,418

    greybeard360
    Member

    If you are talking about the port on the choke thermostat, that should go to the exhaust for heat. Not into the exhaust... Pulling heat from it. The factory manifold had a provision for the tube that allowed heated air to go thru to the carb.
     
  3. cshades
    Joined: Sep 2, 2011
    Posts: 467

    cshades
    Member
    from wi

    Dave, those are supposed to have vacuum to pull heat through a tube in the exhaust manifold to heat and open the choke thermostat. If you have the chokes held open, have manual choke or using electric thermostat you can plug them off. If you are using the factory style choke you will need to figure out how to make them pull heat from the exhaust manifold.
     
  4. 1pickup
    Joined: Feb 20, 2011
    Posts: 881

    1pickup
    Member

    Thanks Chris. I don't see any provision for the stove tubes on the exhaust manifold. I assume they were different manual choke vs. automatic choke. On the lower part of the intake, just above where it bolts to the exhaust manifold, there is a threaded hole (not all the way into the plenum) that I have no idea what it's for. It's only an inch or so away from the exhaust manifold. Think that would work well enough? I don't want to have to make some sheet metal abortion to make it work. Or, I suppose I can just make the chokes stay open...
     
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  5. cshades
    Joined: Sep 2, 2011
    Posts: 467

    cshades
    Member
    from wi

    there should be 2 holes next to each other or at least all the way through the manifold. You could always run 2 manual choke set ups under the dash to the carbs.
     

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