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fuel press into carb, how many PSI??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue Meanie, May 23, 2002.

  1. Blue Meanie

    Blue Meanie Registered Member

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    ok, i just swapped from tbi to carb and i have heard everyone say 6 psi of fuel pressure. now is that 6 psi with the motor off or 6 psi while running? i have it set at 6 psi while off and when i gun it with no load on the motor, it drops down to 1-1 1/2 psi. is that normal? and if not, what should be normal? also, i have no kickdown now, but when it is in 3rd (th400) and i gun it, it starts to knock BAD!! my timing is set at 8D without the vacuum hooked up. when i hook it up, it stays at 8D. shouldn't it go down? and will that cause it to knock under load or does it have too much or not enough gas? again, thank you for the help. i don't know what i would do without this site!!!
     
  2. TopOff

    TopOff 1/2 ton status

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    What year is your distributor?
    Maybe your distributor is not the mechanical advance? Where the computer controls the advance???

    You should be running 6 psi fuel pressure (or less for off-rad) with the engine running.

    What is your fuel pump? Hopefully not the factory TBI... you will need a return line. I believe the factory TBI pump puts out ~20-40 PSI.

    What carb are you running?
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Factroy TBI should be around 12-15 PSI so I've heard.
     
  4. Stoopalini

    Stoopalini 1/2 ton status

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    The TBI in my '92 camaro 305 (LO3) is stock at 11.5psi. I've got a adj regulater and bumped it up to 13 and it runs pretty good with that.

    Thomas.
     
  5. m j

    m j 1/2 ton status

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    THE REGULATOR SETS PRESSURE

    the rest seem to have not read the question

    does the pressure momentarily drop or stay low?
    what kind of regulator are you using?
     
  6. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    At idle, my Carter electric fuel pump puts out 3.5 - 4 PSI at the needle and seat. I've never bothered to checked what it botttoms out at at WOT, but I've never experienced fuel starvation symptons, either.

    I do know that 4 PSI is tons for my 84 305.....
     
  7. TopOff

    TopOff 1/2 ton status

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    --------------ok, i just swapped from tbi to carb and i have heard everyone say 6 psi of fuel pressure. now is that 6 psi with the motor off or 6 psi while running?

    *********6 PSI with it running.

    -------------i have it set at 6 psi while off and when i gun it with no load on the motor, it drops down to 1-1 1/2 psi. is that normal?
    --------------and if not, what should be normal?

    ********** I have no idea why your pressure would drop to 1 1 1/2 psi when you gun it. Unless your carb is going through a lot of fuel, and the fuel bowl is getting a lot of fuel to fill up.

    ----------------- also, i have no kickdown now, but when it is in 3rd (th400) and i gun it, it starts to knock BAD!! my timing is set at 8D without the vacuum hooked up. when i hook it up, it stays at 8D. shouldn't it go down?

    **************I presume 8D is 8 degrees before TDC. IF you have a computer-controlled Distributor (previous TBI system), the computer will advance this as you go through the RPM range. If the computer is NOT hooked up on this computer-controlled distributor, it will not advance and hence you will get REALLY BAD performance!

    ------------------ and will that cause it to knock under load or does it have too much or not enough gas?
    Again, thank you for the help. I don’t know what I would do without this site!!!

    ****************I would think it is very likely that you will get some knock under load or other issues if your timing is not advancing.

    I would get a timing light and see what timing you get at ~2000 – 2500 rpms. That will answer many questions.
     
  8. Blue Meanie

    Blue Meanie Registered Member

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    ok, i am using the stock fuel pump (tbi) and am using a malory press rer with a return line hooked up. i set it to 6 psi while running and things seem to be good. next, i have an 84 distributer, HEI, not that crappy computer controlled junk that came in it. as far as the timing goes, i have it set at 8 btdc. the reason it was knocing the first time was because the timing slipped out. when i thought i was tight on the hold down, i was just hitting the vacuum advance with the wrench, and yes, i am that stupid some times. i have things running good now. thanks for the help.
     

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