Help me pick my next Carburetor please!

Discussion in 'Engine Topic' started by Vortec80, Mar 4, 2019.

What Carb should I use out of these?

  1. Holley 670 street avenger

    6.3%
  2. Holley 750

    68.8%
  3. My current Holley 600

    0 vote(s)
    0.0%
  4. Other...Please drop other suggestions in the thread

    31.3%
Multiple votes are allowed.
  1. jvle95

    jvle95 Veteran Member

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    I have a QF Slayer 750 Vac Sec and I have battled that thing since day one. Very rich at idle, mixture screws are only turned out maybe 1/4 turn. I have tried air bleeds, adjusting secondary throttle plates, checked and rechecked transfer slot and I can not get that thing from being very very rich. Power Valve good, tried different IFR's, the list goes on, lol. Right now I have it all back to stock settings and I am trying to go at it one more time. Even getting the secondary opening dialed in has been a pain. It supposed to be easier with their screw adjustment but I haven't found that sweet spot yet. I can not figure out why that thing keeps dumping so much fuel at idle. Good luck to you and I am curious to find out what works for you. That Holley 650 VS sounds interesting. I may look into that or possibly bite the bullet and give the Sniper a try.
     
    1980RS likes this.
  2. jeff swisher

    jeff swisher Veteran Member

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    I see so many people buying these new fancy name carbs.
    I think the name sells them.
    Fancy like Slayer or Demon.
    The old school carbs have done me well for decades and I do not plan on upgrading.
    Never had an issue with too much fuel at Idle.
    Only issue I had was lack of air flow.
    A grinder or a different size carb fixed that.
     
  3. jvle95

    jvle95 Veteran Member

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    I couldn't agree more Jeff. Sometimes I learn the hard way, such is life.
     
  4. jeff swisher

    jeff swisher Veteran Member

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    I hear you on that.
    I started with carbs when I was about 10 years old.
    I learned to make them work at least the ones I had (say LawnBoy)
    And as I got into cars and motorcycles I made them work also.
    People would give broken motorcycles and cars for free because they knew I would tweak until I got them running.

    I know the new shiny stuff is alluring but I was beating up on my buddies with my JUNK!
    They had new shiny stuff I had carbs from 1960's and they ran excellent. I could not bring myself to buy what they had when I was running much better all the time in all weather conditions.

    When they would break down or need an extra vehicle I was the one to call.

    I had friends that wanted to trade me vehicles for a day..I could not stand the way their vehicles ran and looked so when they got them back they would be detailed and tuned up.

    My brother-in-law called a couple times and asked if I needed to borrow his truck.
    Yep it was running poor and needed cleaned.
     
    dave@ztech likes this.
  5. 1980RS

    1980RS Veteran Member

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    A buddy has the fix for that, he take s off the metering blocks (2 if it's a 4 corner idle) then he taps the how in the mail body that feeds the idle slots put a restrictor in there with a hole drilled to .025 and that fixes about 80% of them he says. For a carb that looks to be pretty nice with a lot of nice features, QF's suck.
     
  6. 1980RS

    1980RS Veteran Member

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    Boy, I wish I was in the 530hp range. I think the engine makes about 470hp as the mph is pretty low @111 tq. is most likely in the 550 lbs. range. If it were around 116 or 117 the 530hp number would be closer. The reason I think the Mighty Demon 850 works better is the A/D boosters, every engine I have used that carb on picks up with it. Even my little pump gas 358 went 11.46 with it so I know it just works. I do have on other Holley 850 out on loan that turned out to be a Fuel Curve Engineering carb from wayyyyy back in the late 70's. I used it once and it had a lot of promise to it. The metering blocks have a ton of work done to it and it's too bad as this is the 2nd one of those I have had and will never sell it, made that mistake once.
     
  7. green

    green New Member

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    Look up Bigs performance on the web. He has a Facebook page and sells on Ebay as well. Have all your engines build specs available. Dont bullshit him with false specs either. He will build a perfect carb for you for about the same as you can buy from a hot rod shop. He will also use your carb if you have one in the cfm he needs. I've seen first hand an increase of almost 40 hp out of the box. Swapping out his for one that was tuned, on dyno, for an engine build challenge. I will never buy off the shelf again
     
  8. G72Zed

    G72Zed Veteran Member

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    jvle95, sounds like you have touched on all the key area's. You mention the PV being good, I will assume PV cavity is dry when taken off the metering block, if not, that would indicate a leak of some sort, and may give the overly rich condition you are experiencing.

    1980RS has a key point on the main body.

    Another point I will share, I have repaired a dozen or so "Fancy Billet" metering blocks that appeared to be completely machined correctly, only to discover they were "short drilled". This caused rich and drivability AFR issues with the owners of these new "highly optioned" carbs. If not already done, I would suggest you "pin" all the emulsion holes and especially the upper kill/anti-siphon bleed and check to make sure they are completely drilled and intersecting fully with the main well. They are usually in the .028-.029 sized area.

    Hope this helps.
     
  9. K1ng0011

    K1ng0011 Veteran Member

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    I agree with some of the others. The Street Demon Carb series is pretty good. I personally had the 625 on my engine but they do have a 750 model, too. The fuel bowl is made of a material that is suppose to help the fuel from getting to hot. You can adjust the rate that the secondaries open with just a screw driver and a wrench which is pretty nice. There are three positions for adjusting the accelerator pump shot that you can use. The metering rods are easily accessible from the top of the carb. There is also a kit you can get with different jets, metering rods, and springs.

    Street Demon Carb: https://www.holley.com/products/fuel_systems/carburetors/demon/street_demon/parts/1901
    Street Demon Calibration Kit: https://www.holley.com/products/fue..._bleeds/tuning_and_assortment_kits/parts/1921
     
  10. jvle95

    jvle95 Veteran Member

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    Good points from all, thanks. PV cavity is dry. I will look into all these pointers. Don't want to high jack the thread.
     

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