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Thread: Couple tuning questions
          
   
   

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  1. #1
    josh bichard is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: 64 chevy stepside
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    Couple tuning questions

     



    Hello everyone. Well, I now no that my distributor has a centrifigul advance. I read about it in the jegs catalog that I ordered it out of. I know I should of noticed that when I bought it, Ive done stupider things. Anyway, how do I know that it works and how can I adjust it? I don't know that it needs adjusted, but it is adjustable. The part number is 555-40005.
    I am also thinking of jetting my carb and had a question about that. The carb is a 700 cfm double pumper. When ever i pull a plug to see how it is running, do I change the primary jets only or do I also change the secondary jets? Should I have different size jets in the primaries and secondaries or the same? Thanks for your time.

    Josh

  2. #2
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    Car Year, Make, Model: '67 Ranchero, '57 Chevy, '82 Camaro,
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    What distributor is that Josh??? If it's an adjustable vacuum advance, there will be an Allen screw inside the little nipple where the vacuum advance connects. The mechanical advance is adjusted by changing the combination of springs and advance weights..... To determine if adjustment is required, you will need to know the rpm that each timing advance event (vacuum and centifugal) begins to come in, and is full in...This you will have to check with a timing light and the engine running....

    The jets, front to rear, should be different sizes with the secondary jets being larger. As a general rule, you would go down one size on each end to lean the carb out a bit...Depends really on how the car is performing. If it's rich a cruise RPM, but works great when you floor the pedal, then only a change in the primary jets would be necessary. Jetting is mostly a matter of one or two jet sizes at a time followed by a test drive....Unless you have an Air/Fuel monitor. I cheat, and do mine on Andy's chassis dyno!!!!!!Really nice to have friends with expensive tools!!!!
    Yesterday is history, tomorrow is a mystery, Live for Today!
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  3. #3
    josh bichard is offline CHR Member Visit my Photo Gallery
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    The description says it has an adjustable centrifigul advance. It is the jegs street spark hei

  4. #4
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    Yup, the vacuum advance should have the adjustment I mentioned and the centrifugal is done with the springs on top of the advance mechanism under the rotor. Pat McCarthy probably has the right spring setup for it, but first you'll need to know where the timing is coming in at on the revs.....
    Yesterday is history, tomorrow is a mystery, Live for Today!
    Carroll Shelby

    Learning must be difficult for those who already know it all!!!!

  5. #5
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
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    Is that for your Ford or your Chev????

  6. #6
    josh bichard is offline CHR Member Visit my Photo Gallery
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    its on the 350

  7. #7
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
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    carb 4778????

    try 68 primary with around 4.5 powr valve and maybe up to 76 seconary---check the way the fuel flows from accerate pumps as carb opens

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