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  1. #1
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    Default Quick fuel Block in Street Avenger

    I just stuck one of those QFT metering blocks in a SA670 and it is idling pig rich with screws 1/4 turn out. It's got four emulsion bleeds and no ported vac. Have I bought the wrong block? ....any thoughts

  2. #2
    Senior Member BasicQ's Avatar
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    Default Quick fuel Block in Street Avenger

    IFR in upper position is probably mid thirty thou and with the 1-1/4” venturi and 1-9/16” throttle plates on the primary something like .028” IFR would be better.


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    33 thou, but I've soldiered and drilled ifr to 27thou but its still stinking rich,shaking and wont idle,must be sucking fuel from elsewhere.

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    Senior Member BasicQ's Avatar
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    Default Quick fuel Block in Street Avenger

    Idled ok with previous metering blocks? I assume you went to .027” IFR because that’s what the original blocks had? And it idled ok before installing the QFT blocks without excessive transfer slot exposure and the idle air bleeds it has now? 4 corner idle?

    What I am getting at is, is the metering block the one and only change and idle has gone from good to worse?


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    Last edited by BasicQ; 06-05-2021 at 09:52 PM.

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    Senior Member BasicQ's Avatar
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    Default Quick fuel Block in Street Avenger

    Are the x4 emulsion.028”, .028” block, .028”?

    Might sound a bit odd but I have had on 5 hole emulsion where positions 1 & 3 were open and the others blocked and then changed nothing but adding open emulsion to the bottom position and idle changed. And the bigger that bottom emulsion hole the more the effect. Went a tad richer.

    Compare the height of lowest emulsion and where idle fuel is drawn from the main well against the original block. If the original is higher then with the QFT there may be more fuel head pressure allowing fuel to be drawn through the idle circuit easier. If this is the case maybe even smaller IFR are needed.


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    i think BasicQ is onto it, emulsion height and location differences will dictate what size IFR is needed id say around .025 may be needed with that type of metering block

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    Senior Member BasicQ's Avatar
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    I’d also suggest getting more un-drilled blanks and start with top down .028” x .028” x as a baseline then trial .028” .028” x x and then as delivered by Quickfuel to discover what part throttle appetite your engine has.

    Do you know main air bleed size?

    I get all my idle/emulsion bleeds from Summit. I get Quickfuel brand as they are the most economical and have whatever size you want. You just have to wear the postage cost. I usually add them to a larger order to justify the cost a bit more.

    If you can find them locally or better yet a suitable blank set screw then all the better.


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    Quote Originally Posted by BasicQ View Post
    Idled ok with previous metering blocks? I assume you went to .027” IFR because that’s what the original blocks had? And it idled ok before installing the QFT blocks without excessive transfer slot exposure and the idle air bleeds it has now? 4 corner idle?

    What I am getting at is, is the metering block the one and only change and idle has gone from good to worse?


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    Yes,it idled fine with previous block with 0.3mm wire in IFRs.And yes,the IFRs are lower on the QF block. Holes 1 2 4 are 23thou with 3 blanked. I've now noticed a QFT block thats same as standard block but with screw-ins....should I have used this block?????
    Yes,carb is still four corner idle and the block was only change...
    Last edited by 71rocket; 07-05-2021 at 04:48 PM. Reason: extra info

  9. #9
    Senior Member BasicQ's Avatar
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    Default Quick fuel Block in Street Avenger

    So doing some calculations if the original block had .028” (0.711mm dia) IFR and you inserted .3mm dia to restrict then that’s a reduction of almost 19% in area or equivalent of reducing to approximately .023” IFR. Now having .027” in the new block with the influence of extra low emulsion then it’s a bit clearer why it’s rich.

    Is the blocks p/n something like 34-4QFT? It has threads in the 3 unblocked emulsion doesn’t it? You will get the block to work and likely better than original due to the extra flexibility to dial-in to your combo, but what comes with the benefit of adjustability is some work to get there in the end. I know you are already trying to source bleeds or at least blanks to drill. They are a must to realize the blocks and therefore your engines potential as an adjustable metering block with fixed .023” emulsion orifices is by definition not adjustable. Had you bought the other block with screw-ins tuning would still be the same.

    I am also a fan of having primary and secondary metering balanced especially for WOT so when the primary is dialed in replicate on the secondary.

    I reckon being a vac sec the secondary iab will be small and in the area of .030” - .040”. This will contribute to rich idle too. If you have a secondary metering block with the same IFR as the primary then open up secondary iab to the same as the primary. I wouldn’t be surprised if Holley are being cost effective and use that same main body with press in bleeds with other models without secondary metering blocks. This info is a bit late in the feedback but important for idle balance with 4 corner idle.


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    Last edited by BasicQ; 07-05-2021 at 08:09 PM.

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    Quote Originally Posted by BasicQ View Post
    So doing some calculations if the original block had .028” (0.711mm dia) IFR and you inserted .3mm dia to restrict then that’s a reduction of almost 19% in area or equivalent of reducing to approximately .023” IFR. Now having .027” in the new block with the influence of extra low emulsion then it’s a bit clearer why it’s rich.

    Is the blocks p/n something like 34-4QFT? It has threads in the 3 unblocked emulsion doesn’t it? You will get the block to work and likely better than original due to the extra flexibility to dial-in to your combo, but what comes with the benefit of adjustability is some work to get there in the end. I know you are already trying to source bleeds or at least blanks to drill. They are a must to realize the blocks and therefore your engines potential as an adjustable metering block with fixed .023” emulsion orifices is by definition not adjustable. Had you bought the other block with screw-ins tuning would still be the same.

    I am also a fan of having primary and secondary metering balanced especially for WOT so when the primary is dialed in replicate on the secondary.

    I reckon being a vac sec the secondary iab will be small and in the area of .030” - .040”. This will contribute to rich idle too. If you have a secondary metering block with the same IFR as the primary then open up secondary iab to the same as the primary. I wouldn’t be surprised if Holley are being cost effective and use that same main body with press in bleeds with other models without secondary metering blocks. This info is a bit late in the feedback but important for idle balance with 4 corner idle.


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    Yep 34-4 pn.It shakes and heaps of peddling just to keep it running,not jetting,drowning in fuel.Previously been using an old 600vac block and today measured the IFRs around .026-.027 so with 0.3mm wire must be pretty lean but is smooth at idle and very light throttle,,,rear screws 1 turn out and 1 1/2 on prims. I want the QFT to adjust the PVRs,I can live with the bits of wire.

  11. #11
    Senior Member BasicQ's Avatar
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    That does seem like more than just an orifice size issue. One thought is fuel pressure too high dripping fuel from the booster but I assume nothing was changed there regarding fuel delivery pressure. Another is power valve vacuum receptacle area sealing off. This is nothing to do with the power valve rating but the round power valve gasket not leaking (they are sometimes laminated to make a thick gasket from thinner material and the layers can separate when tightening) and the power valve itself not leaking. Might also need close inspection of the metering block gasket sealing the vacuum source area on the main body.

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    Quote Originally Posted by BasicQ View Post
    That does seem like more than just an orifice size issue. One thought is fuel pressure too high dripping fuel from the booster but I assume nothing was changed there regarding fuel delivery pressure. Another is power valve vacuum receptacle area sealing off. This is nothing to do with the power valve rating but the round power valve gasket not leaking (they are sometimes laminated to make a thick gasket from thinner material and the layers can separate when tightening) and the power valve itself not leaking. Might also need close inspection of the metering block gasket sealing the vacuum source area on the main body.
    Fuel pressures at 6 and the QFT power valve uses an o-ring rather than a gasket but I'll check that and block gasket. thanks for help

  13. #13
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    Quote Originally Posted by BasicQ View Post
    That does seem like more than just an orifice size issue. One thought is fuel pressure too high dripping fuel from the booster but I assume nothing was changed there regarding fuel delivery pressure. Another is power valve vacuum receptacle area sealing off. This is nothing to do with the power valve rating but the round power valve gasket not leaking (they are sometimes laminated to make a thick gasket from thinner material and the layers can separate when tightening) and the power valve itself not leaking. Might also need close inspection of the metering block gasket sealing the vacuum source area on the main body.
    This^^ I would be checking metering block gasket is sealing both sides, as cross leaking will do as you describe, and then the PV and gasket, as Basic stated.

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    Quote Originally Posted by EH179 View Post
    This^^ I would be checking metering block gasket is sealing both sides, as cross leaking will do as you describe, and then the PV and gasket, as Basic stated.
    Will do,then I'll throw the QFT block in the bin along with the JP hi vol pump,holley blue pump and all the other after market crap Ive bought.....starting to think LS1 with efi.

  15. #15
    Senior Member BasicQ's Avatar
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    Default Quick fuel Block in Street Avenger

    Quote Originally Posted by EH179 View Post
    This^^ I would be checking metering block gasket is sealing both sides, as cross leaking will do as you describe, and then the PV and gasket, as Basic stated.
    I should have added the pv gaskets are thick is to avoid the threads bottoming out in the female block thread and not clamping down on the gasket before becoming tight if there is insufficient thread on the pv. If the o-ring is not proud enough or pv has a thread that is not long enough there will be insufficient crush onto the o-ring.

    (Oops, quoted the wrong post!)

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    Last edited by BasicQ; 08-05-2021 at 07:39 PM.

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