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ATTN: Holley carb folks

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KRAZIE87K5, Dec 20, 2001.

  1. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    I have this great QJet that I acquired, but I can't locate the correct adapter. SO - I am stuck with the Holley that I currently have for now.

    The problem is, when I step on the gas ( no matter how hard or soft ), the engine feels "weak" for a second or two until something catches up, then the power comes in full tilt. I also have a problem with the darn thing "popping" for no reason under steady throttle. This sounds like a small back-fire, but is nowhere near as intense.

    My timing is a 8* at 900RPM. 7lbs fuel pressue at the regulator. This is a 750cfm Holley double-pumper. Exact model number unknown from my desk at work. [​IMG][​IMG]

    Any ideas? Or does anyone have the correct adapter to get a QJET installed on a squarebore intake?

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  2. DesertDueler

    DesertDueler 1/2 ton status

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    Mecanical or vacuum secondaries? Also your fuel pressure is a little high, try 6 psi and see what happens. The popping can also be caused by the power valve being blown out. I have had the same symptoms happen wen I blew a power valve in the firebird.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  3. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Mechanical secondaries... [​IMG] I'll back off the fuel pressure to 6 and see what happens.

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  4. DesertDueler

    DesertDueler 1/2 ton status

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    They are great carbs for power. If that doesnt work then I bet its the power valve. The only problems I only have had a few problems with that carb in three years, one the power valve, and two the fuel pressure was too high and would push fuel past the needle and seat.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Its funny that you say that... this weekend, I started the truck to let it warm up and went back into the house. Came out 10 minutes later, and the engine had stalled out. The electric fuel pump was still running, so I assumed nothing bad...

    So I hop in, turn the key, and it goes, "ruh, ruh, clunk!" I let the key go. I have locked motors in the past. I was scared. I turn the key again, and "clunk". My heart sunk. I hop out and start swearing... looking on the ground for fluids. Didn't notice anything, until I smelled the fuel in the air.

    I open the hood, and the fuel is dripping off the Holley! Think to myself, "Well that can't be too good!" Proceeded to pull and replace the plugs, and change the oil.

    Hopped back in, and "Vvvvroom!" Started right up like always. After a few minutes of burning leftover fuel from the exhaust pipes, she ran like new.

    I also gapped the plugs to .060 with good results!

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  6. DesertDueler

    DesertDueler 1/2 ton status

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    Get a new power valve too, just to be safe. You will have to pull the front bowl off and the metering block to find out the numbers on it though. When a power valve blows out its like adding 10 jet sizes. It will make it run extremely rich.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  7. michaelm

    michaelm 1/2 ton status

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    is the timing sound?
     
  8. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    The timing is all good... The power valve on the other hand... that could certainly be the issue... Is there anyway I can look at it to visually determine if its good or not?

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  9. michaelm

    michaelm 1/2 ton status

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    a power valve is a rubber diaphram that is vacuum controlled.
    can you post the # from the choke horn of your carb?
    I can look up what it should be.
    did the carb run good at one time and the trouble has just begun?
    you are guessing it is a lean pop not timing related?
     
  10. michaelm

    michaelm 1/2 ton status

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    <a target="_blank" href=http://members.juara.com/carnut/tech/pwrvlv/>http://members.juara.com/carnut/tech/pwrvlv/</a>
    I doubt the powervalve is the problem unless you had a big backfire recently that may have torn the diaphram
     
  11. michaelm

    michaelm 1/2 ton status

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    sounds like you need an oil pressure switch to turn the pump off when the engine dies
     
  12. DesertDueler

    DesertDueler 1/2 ton status

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    Its not true on the car not idleing. Mine idled fine, but ran extemely rich.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  13. 502Burban

    502Burban 1/2 ton status

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    If it's a 750cfm double-pumper like it sounds, it is probably the 4779 carb. IIRC, they come with a 6.5" power valve. It's kinda gross, but I always used to check 'em by just putting the flat side to my mouth (after blowing dry/clean with air) and apply suction (alright, no jokes about that, please[​IMG]) to the valve to see if the plunger will move. If it moves, it's fine. If not, no good.

    To get the proper valve, I've always taken a vacuum reading at idle, and sized the power valve 1.5" lower. For example, if you are pulling 10" of vacuum at idle, go with a 8.5" valve.

    77chev, please correct me if I'm wrong. I know you are good with these things and it's been years since I played with a Holley. I know most on this board hate them, but like most things, they work great if a person takes the time to figure them out.[​IMG] I always had good luck with them, drag racing or wheeling, myself.

    Robb
    <a target="_blank" href=http://community.webshots.com/user/robbrj>'73 GMC Suburban - 502DFI</a>
     
  14. 502Burban

    502Burban 1/2 ton status

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    Just re-read your post, and a couple other things come to mind. I agree that your fuel pressure should be no more than 6psi, and I've always liked the spring-loaded needle &amp; seat for wheeling. They're less likely to flood, generally.

    Also, based on the mild back fire under partial throttle increase, you may have a misadjusted or dead accelerator pump. Check to see if you get a squirt of fuel when you rev the engine. Please be careful to keep your face away from the carb, though. A friend still has no hair from a carb backfire.[​IMG] If it squirts OK, check to make sure there isn't a lot of freeplay at the accelerator pump lever.

    Hope some of this helps,

    Robb
    <a target="_blank" href=http://community.webshots.com/user/robbrj>'73 GMC Suburban - 502DFI</a>
     
  15. 502Burban

    502Burban 1/2 ton status

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    I definitely second that motion! Gotta have a oil pressure safety switch with an electric pump and carb combo.[​IMG]

    Robb
    <a target="_blank" href=http://community.webshots.com/user/robbrj>'73 GMC Suburban - 502DFI</a>
     
  16. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    DId you adjust or at least check the float bowl level on the primarys and secondaries after you saw gas leaking from the carb?

    I agree... the off idle sputter or pop is probally related to that accelerator pump... IT happens when you get on and off the gas right?
    It could be defective, clogged, misadjusted...
    There are like a dozen different accelerator pump cams available to fine tune that off idle sputter... It's usually a lean miss because those butterfly valves open so fast there is not enough fuel to keep up with that amount of air... so theres a sputter until it recovers and gets enough fuel from the jets. The accelerator pump shot of fuel is to compensate for that.
    With that said... ususally being a lean sputter, you can go up in size to a larger accelerator pump cam and get rid of that.

    ...But that is if you even want to invest any time or money into that carb... You probally just want to get rid of it and put that QJet on!!!
    Hey I'll buy that Holley from ya for say $5 plus shipping? eh?[​IMG]

    [REAL MEN DON"T CARE ABOUT GAS MILEAGE OR RAPID TIRE WEAR!]
    Ryan B.
     
  17. Pure Insanity

    Pure Insanity 1/2 ton status

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    I am having a similar prob w/ the Holley in mine. Only difference is that my carb only shows its butt and stumbles just barely off idle. If I am trying to barely roll along for example. If I am making a "normal" take off from a lite, it takes right off no problem. I have a bad metering block, which is causing a different problem, (according to a mechanic at the shop that builds roundy round cars.) All the info provided is all good advice. Make sure the accelerator pump is shooting as you roll into the throttle. My off idle stumble is because mine is not shooting unless it gets a sharp hit, no matter how small, it must be a quick hit to the pump. I have adjusted the linkage, but it doesnt change. I am thinking it is the pump return spring inside the pump housing.

    If ya can't stop.......Smile as you go under! [​IMG]
    PIC of mine from flblazers site<a target="_blank" href=http://www.flblazer.alloffroad.com/photo3.html>
    GO</a>
     
  18. Thunder

    Thunder 3/4 ton status

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    Heres the adapter you need <a target="_blank" href=http://www.proformparts.com/catalog/carb_adapters.html>Peformparts.com/carb adapter</a> Part#66251 should work fine for you.. I'v used similar adapters when installing Q-Jets on fords and jeeps. They worked good and didn't seem to restrict the flow much.
    Also a company called Specter makes those adapters too. I think Checker, Kragen, Shucks carry them or can order one.


    If your Holley has vacume operated secondaries. You may need a heaver spring in the vacume module. If the secondaries open too soonYou will loose manifold vacume and lean out the fuel mixture and that can also cause a stumble on aceleration. A heavier spring willl keep the secondaries from opening till the RPMs get higher. You can get a kit that has about 6 diferent size springs so you can fine tune the carb.
    <P ID="edit"><FONT class="small">Edited by Thunder on 12/20/01 07:16 PM.</FONT></P>
     

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