Power valve

Discussion in 'Holley' started by Romel, Jul 10, 2019.

  1. Romel

    Romel Well-Known Member

    I have a 870 holley with vac secondaries. It has a 6.5 valve in front and a 3.5 valve in the rear. Is this right. Seems odd to be that big of a difference. Its a duel feed. Thanks. My four barrel just dont seem to work right and i have changed springs and cams.
     
    Last edited: Jul 10, 2019
  2. hugger

    hugger Well-Known Member

    sailbrd likes this.
  3. hugger

    hugger Well-Known Member

    Looks like one part # has a 3.5 PV In the rear Screenshot_20190710-235314_Drive.jpg
     
  4. hugger

    hugger Well-Known Member

    Part # 80870 was originally a 4.5 in front and 3.5 in rear with the pink spring
     
  5. Stevem

    Stevem Well-Known Member

    Since your playing with springs and pump Cams are you getting a stumble from the Carb just off idle, or are the secondary's giving you a stumble when you dip hard into those?

    Ifits a off idle thing then your idling too much off of the primary's and there's a few ways to cure that depending if the Carb has replaceable idle air bleeds on it?

    Here's a basic low down on Holley fuel feed circuits.

    If so you have the primary In a Holley where there are 3 main fuel supply circuits.
    There is the idle circuit which comprises the mixture screws, the idle air bleed jets on the top of the Carb , and internal the emulsion tube and the transition slots in the throttle plate.

    Next up are the main jets as you start to get deeper into the throttle opening, and after that once the vacuum drops enough to start to open the powe valve then the size of the power valve restriction channel in back of the power valve starts to pass fuel.
    You need to determine what circuit of the Carb your issue is part of .

    All too many folks will kick up the main jet size to make the overall full throttle mixture richer , but this will make for your you mid throttle range to be too fat if it does not need to be.

    A 3.5" power valve on the secondary side my be fine, but the only way to truly find out such for any given motor it to hook up a vacuum gauge with a long ass hose such that you can see it while you drive and as you dip into the secondary's going open.
     
    Last edited: Jul 11, 2019
  6. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    if playing with PV selection also be aware that the lower number power valves open at a higher rpm ( less extra fuel down low and midrange ) than the higher range PV numbers .
     
  7. Romel

    Romel Well-Known Member

    Thanks everyone
     
  8. shiftbyear

    shiftbyear Well-Known Member

    Is there a certain RPM that the carb does not perform well?
     
  9. Romel

    Romel Well-Known Member

    Its not opening the four barrel until about 5 seconds after flooring it. At all rpm levels
     
  10. Stevem

    Stevem Well-Known Member

    Something is way wrong with those vacuum secondary's if your telling me that even up above 4000 rpm it takes seconds for them to open!
    What color spring is in the the thing?

    Are the secondary throttle blades hanging up like the Carbs throttle plate is bent or twisted?
     
  11. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    on a small block the stock/oem spec spring does not allow the secondary's to fully open until around 8000 rpm . a little dif for a big block . that is per the holley book .
    I recommend the next step better spring ( purple ) or 2 step better is the long yellow spring . depending upon your driving those rpm ranges seem better suited .
    the quick fuel adjustable vac sec unit I like comes preset with the purple spring . the couple times I've run those they were good right out of the box .
     
  12. Romel

    Romel Well-Known Member

    Thanks guys. I put everything back to factory specs and it still didnt work right so i gave up and bought a new quick fuel brawler instead. Again thanks for the replies
     
  13. hugger

    hugger Well-Known Member

    The Brawler running better
     
  14. Romel

    Romel Well-Known Member

    I wont have it until Friday. I will post how it runs. Hopefully better then it did
     
  15. Romel

    Romel Well-Known Member

    So i got the brawler on Friday afternoon and put it on. Wouldnt even start. Both bowls were full over the sight glass and 3 of the air bleeds were screwed all the way in. I finally got the bowl levels set right and the air screws set. Started right up and idled fine. Took it out on the road and has massive stumbling at take off and full throttle. Not very happy with quick fuel right now. Ready and set up to run out of the box. Bulls##t
     
  16. hugger

    hugger Well-Known Member

    What part # did you get?
     
  17. Romel

    Romel Well-Known Member

    It is the BR-67214. 850 DP with mechanical secondary
     

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