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Vac reading

Discussion in 'The Garage' started by adamforsythe, Feb 27, 2006.

  1. adamforsythe

    adamforsythe 1/2 ton status

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    I hooked a vac gauge up to my carb and I am reading 5 at idel and 15-25 while reving.
    What should I be reading????? School me on vaccum.
    Thanks
    Adam
     
  2. 1979jimmy350

    1979jimmy350 1/2 ton status

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    you must have hooked it up to the wrong port becasue you should have a higher reading at idle, hook it up to a port that uses vaccum after the throttle plates not before
     
  3. adamforsythe

    adamforsythe 1/2 ton status

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    I'll hook it up to the intake this weekend. It's way to cold to do it now. What kind of stuff will the gauge tell you? I know it will tell you if you have a leak ( How ).
    Thanks
    Adam


     
  4. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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  5. 77crewcab

    77crewcab 1/2 ton status

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  6. adamforsythe

    adamforsythe 1/2 ton status

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    Thanks for the info guys. I think I am smarter when it coes to reading a Vacuum Gauge. :p:
    Thanks
    Adam
     
  7. trailblazr81

    trailblazr81 1/2 ton status

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    Ive learned the ways of the vacuum gauge and always use 'em to tune carbs. :waytogo:
     
  8. adamforsythe

    adamforsythe 1/2 ton status

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    I just hooked my intake up to the gauge and I am reading 20 at Idel and if I gun it it drops down to 5, If I rev up slowly it stayes in the 20-25 range. The gauge does not sway between numbers at idel or if I hold the Rpms off from idel.
    Thanks
    Adam
     
  9. adamforsythe

    adamforsythe 1/2 ton status

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    How would i go about adjusting my carb with it????????
    Thanks
    Adam

     
  10. trailblazr81

    trailblazr81 1/2 ton status

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    Hook up vacuum gauge to a port on carb with constant vacuum. Turn in idle screw to lean it out. Do maybe 1/4 turn at a time. Do this till you get max vacuum. But remember every time your RPM's increase, lower them back down to original idle RPM. You want both idle screws (or 4 depending on carb type) to be about the same. So adjust one then the other, keep going back n forth. 1/4 turn left screw, 1/4 turn right screw... And of course different engines with different cams will have different vacuum readings. If she stumbles fatten 'er up 1/4 turn.
     
  11. trailblazr81

    trailblazr81 1/2 ton status

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    You are at 20 at idle, yet after tuning my 388 with cam I never got above 16.
     
  12. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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  13. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    its a good article.... i guess it pays to save that stuff... my tech folder has gotten quite large.... :haha:
     
  14. adamforsythe

    adamforsythe 1/2 ton status

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    Hello,
    Sweet thanks for the info.
    Thanks
    Adam

     
  15. adamforsythe

    adamforsythe 1/2 ton status

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    Trust me i am saving EVERY link.

     
  16. HarryH3

    HarryH3 1 ton status Author

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    Cam selection has a HUGE impact on idle vacuum. Altitude also affects it. Here at 7,000 feet I only get about 13 inches at idle with my 383. :eek1: My stock TBI 350 reads closer to 17 inches.
     
  17. walla2k5

    walla2k5 1/2 ton status

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    Great info guys,thanks...
     

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