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Technical Chevy Rochester Tri-power

Discussion in 'Traditional Hot Rods' started by windrider_34, Aug 30, 2019.

  1. windrider_34
    Joined: Apr 16, 2010
    Posts: 7

    windrider_34
    Member
    from Iowa

    It’s a 35 Ford pickup running a 350 crate engine, mild cam, Offy intake and (3) Rochesters (middle 2gs, other 2-2g). It’s running god awful rich!! I have a manual choke and has to be fully closed to start then opens slowly for next 1-2 minutes until the engine is normal temp. Every time I start it afterwards the must be used.
    I’ve screwed the idle mixture screws in a bit. The vacuum gauge runs 12-13 at idle and around 20 at high idle.
    Fuel pressure is 1 1/2.
    Any ideas on how to reduce the rich mixture? Thanks.
     
  2. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,216

    2OLD2FAST
    Member
    from illinois

    Close the throttle blades completely on the front and rear carbs , if they have idle screws they're not proper for a trip power , but close them completely also , idle only off center carb ...
     
  3. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    The Offy is not a very well designed 3-2 intake for any engine. It may take a richer setting to make them run well. I gave 2 away when I found Edel's... There is one guy on the net that can fix the nailhead ones.....Just sayin
     
  4. They work best with progressive linkage.
    The end carbs are supposed to do nothing.
    No air and no fuel nothing until the center is well open and then the end carbs open
     
    olscrounger likes this.

  5. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    I must be misreading this or something, but it doesn't make sense. You say it's running rich, but then you say you have to choke it to get it to start & run. If it was running rich, wouldn't applying the choke (cutting off the air supply) make it even worse?
     
    olscrounger, upspirate, hrm2k and 2 others like this.
  6. Are they set up progressive?
     
  7. I agree it would run rich with the choke on and you shouldn't have to choke the motor if the motor is warm, it should only be when cold starting. Also its not very clear but do you have choke's on all the carbs? You should only have a choke on the middle carb. A picture or two of your setup would help a lot.
     
  8. guitarguy
    Joined: May 26, 2008
    Posts: 650

    guitarguy
    Member

    Agreed on the confusing info. Choke on will run richer. But what caught my eye was only 1.5 psi of fuel pressure? That's like gravity feed type pressure. Sounds to me as if your starving the engine.
     
    Last edited: Aug 30, 2019
  9. hudson48
    Joined: Oct 16, 2007
    Posts: 3,108

    hudson48
    Member

    As said before. Front and rear carbs should not have idle screws. I am running about 3-3.5 lbs. When running use a vacuum gauge on front and rear and should be 0 and middle about 20 from memory. I had a lot of trouble with mine until I reduced fuel pressure.
     
  10. carbking
    Joined: Dec 20, 2008
    Posts: 3,715

    carbking
    Member

    Do you have tags on the carburetors??????

    Knowing WHAT you have makes life much easier.

    Would suggest block-off plates under the front and rear for initial tuning. Maybe that will bring up the vacuum.

    Vacuum in the 12~13 inch range means the economizer valve on the center carb is always open! This will cause excessive richness.

    Check for a vacuum leak (if the block-off plates don't raise the vacuum, do the block-off plates first).

    1.5 psi fuel pressure is probably insufficient, once you get the vacuum issue solved. I used to run about 6 on the tripower on my GTO. At idle, I had 21 inches vacuum.

    Jon.
     
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  11. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    With it idling look down into each carb, the carb(s) you can see fuel is the ones you need to fix. You shouldn't see any fuel anywhere when its idling.
     
  12. windrider_34
    Joined: Apr 16, 2010
    Posts: 7

    windrider_34
    Member
    from Iowa

    No idle screws on front or back.
     
  13. windrider_34
    Joined: Apr 16, 2010
    Posts: 7

    windrider_34
    Member
    from Iowa

    Front and rear are dry as a bone. And I am using progressive linkage.
     
  14. windrider_34
    Joined: Apr 16, 2010
    Posts: 7

    windrider_34
    Member
    from Iowa

    Only have man
    Would low fuel pressure cause gassy situation?
     
  15. windrider_34
    Joined: Apr 16, 2010
    Posts: 7

    windrider_34
    Member
    from Iowa

    Where would I find block off plates? Thanks to all.
     
  16. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,216

    2OLD2FAST
    Member
    from illinois

    Disconnect the front & rear carbs , put some 4mil plastic between the manifold and carbs if you don't want to cut and drill metal for block off plates. I didn't realise that the economizer ( power ) valve opened with that much vacuum (12 -13")
    , you may need to change the spring .....5# fuel pressure should work fine ...
     
  17. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Before you do too much look into the carbs first. It is running on the idle circuits, the front & rear don't have idle circuits so just the center carb is supplying fuel thru the idle circuit - it probably can't get rich enough thru that one idle ckt to get as rich as you describe, that means fuel is entering the carb(s) unmetered, like a float too high. If you look into a carb at idle you shouldn't see any fuel, if you see fuel dribbling out of any of the boosters then that is the problem and the float is too high. Its very easy to get those rochester floats too high and what you are describing is what happens. As I said, you just need to take a long look into each carb to either confirm or rule out the float adjustment.
     
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  18. Piewagn
    Joined: Mar 25, 2009
    Posts: 1,492

    Piewagn
    Member

    If your float levels are not set right, you can get dribbling fuel from the boosters. before you do anything, set your floats accordingly. I had the rich problem, floats were causing the dribbling from the boosters. Also, if you have power valves in the secondaries, that's a big no-no! I did battle with mine and got it running great!
     

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  19. manyolcars
    Joined: Mar 30, 2001
    Posts: 9,176

    manyolcars

    This is the only time I've ever heard of boosters. What are they?
     
  20. Piewagn
    Joined: Mar 25, 2009
    Posts: 1,492

    Piewagn
    Member

    The 2 small venturies above the main where fuel is drawn from the bowl....it;s also known as the cluster....It's where the emulsion tubes and all that's needed to atomize the fuel are housed....
     
    Last edited: Sep 1, 2019
  21. Piewagn
    Joined: Mar 25, 2009
    Posts: 1,492

    Piewagn
    Member

    these.....
     

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  22. X-cpe
    Joined: Mar 9, 2018
    Posts: 1,958

    X-cpe

    What are your clues that it is burning rich? Black smoke out of the tailpipe? Sooty plugs? Exhaust burning your eyes? I believe too lean will also burn your eyes. Did you have a different set-up on this engine prior to the 3x2 that ran OK? Did the 3x2 run OK then go bad? Like stated above the best thing to do is block off the end carbs (and their fuel supply) or completely remove them and sort out the primary carb first. That way you are only dealing with the variables of one unit at a time.
    When checking float levels make sure you don't have a heavy float. Phenolic ones sometimes get cracks and soak up fuel. Brass floats can crack and fill with fuel. Also make sure somebody didn't get too happy with the solder on a prior repair. Make sure the seat is screwed in tight and the needle completely shuts off flow. A 99% test is to try and blow in the fuel inlet. If the float is high enough for fuel to be dribbling out of the main discharge nozzles then there should be some wetness around the the top gasket.
    Have you goosed it a couple of times prior to starting it to check your pump shot? No or weak pump shot could mean the float bowl has drained. Your low fuel pressure could mean it is taking time at cranking speed to refill the bowl and the choke is necessary to create enough vacuum to pull sufficient fuel through the idle ports and main discharge nozzles.
    When you have the top off to check the float setting, check to make sure the power valve is tight and the little pin sticking up is free. Also check the that the power valve piston hanging down from the top cover is free.
    Before starting on the carb(s) make sure the ignition timing is correct.
     
  23. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,216

    2OLD2FAST
    Member
    from illinois

    This may not be obvious to the OP , picture shows 3 different ,separate clusters ...
     
  24. joel
    Joined: Oct 10, 2009
    Posts: 2,467

    joel
    ALLIANCE MEMBER

    Make sure the throttle plates in the end carbs seal off completely when closed; other wise you have an installed vacuum leak. The end carbs have thicker throttle plates than regular 2g carbs and are closely fit to the bores in the carb base.
     
    Tri-power37 likes this.

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