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Thread: NEED HELP tuning a 670 Brawler.

  1. #1

    Default NEED HELP tuning a 670 Brawler.

    I've been pulling my hair out trying to get this carb right. Everything is super close, BUT in order to get rid of the lean spike on light throttle, I ended up closing secondary blades to maybe a 1/8th turn open with the adjustment screw under the carb. If I open the secondaries at all it has the lean spike, I tried for the longest to remedy that with bigger a idle jet and it didn't help as long as the secondary blades were open at all. I tried to open them so I could close the primary blade to get a smaller transfer slot. No matter what I've done it would spike lean unless I close the secondary blades. NOW, the issue I have, since closing the secondary blade is, it's super rich at idle. It's idling at 12.6 now even with 30 IFRs. I also had to drop the low speed bleed to 65s (came with 70s). This gets rid of the lean spike, but now it's rich.
    So either it has the lean spike with secondaries open or it's pig rich with secondary blades closed to get rid of the lean spike. Damned if I do, damned if I don't.
    **********CURRENTLY**********
    Timing is 17° initial.
    36° total.
    7° vacuum advance full vacuum. So 24° at idle.
    Idle -- 12.6.
    Cam is a 231°/236° @ .050" cam. 13 inHg of vacuum at idle. Light cruise -- 13.7:1.
    Carb is Vac secondary Brawler 670. Acceleration -- 14.0:1.
    Orange cam, 31 squirter. Power -- 12.8:1.
    70 primary jet, 78 secondary jet.
    7.5 power valve.
    65 low speed bleeds.
    28 HSB.
    30 IFRS.
    Secondary blades 1/8 turn open.
    Primary blades (transfer slot) is like 40 thousands.
    Engine is a 470 HP 383, Pertronix Ignitor III ignition.
    Am I just stuck with rich idle? Can I increase my vacuum advance to lean it at idle? Thanks.

  2. #2
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    2,074

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    Carb is a bit small for my liking. I would have at least a 750 on there. I'd open the secondaries a fraction more, get your idle cleaned up, and look at accelerator pump cam tuning. And with your carb blade settings now, it sounds like you have a vacuum leak from somewhere else, since this engine should stall with the blades nearly shut. Gary
    Last edited by Gaz64; 03-02-2021 at 06:08 PM.

  3. #3

    Default

    @Gaz64: I do have an almost new AED 750DP I could put on there. The engine builder said it'd be a little too big? The car is a '80 Malibu, 700R4 transmission, 3.73 rear gear.

  4. #4
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    2,074

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    Your combo is similar to a friend of mine. I built his 355 & 750 DP Quick Fuel. He runs a 700R4, 3.9s, and a 26" inch tire. Great package on the street. You have another 28 cubes, so don't be scared of the 750. Just be sure on the transmission kickdown cable fitment.

  5. #5

    Default

    I'll try it cause I'm tired of trying to get this Brawler right. I've literally tried everything. I consider myself pretty good with Holley style carbs. Thanks for the help. Oh and on the TV cable, I'm running a constant pressure valve body.
    I went and drove it again today, and I lean out the idle with the idle screws to get 13:1 at idle, went out and it's at 12.5:1 at cruise, slow throttle opening to accelerate and it spikes to 15:1 and then goes to around 13.8:1.
    It's weird, I have pig rich condition to a lean spike to pretty good on the mains. I don't know, starting to think the metering block is the issue.

  6. #6

    Default

    I think I got it close enough to live with. I gave it more vacuum advance at idle from 23° at idle (with vacuum advance) to 30°. Timing is 17° initial, 36° total. Went to the 32 IFRs, and 67 low speed bleeds. It idles at 12.8:1- 13.1:1, upon cracking the throttle it goes to 14.8:1, but quickly stabilizes at 13:8.1, cruises at 14:6.1. I ended up opening the secondary throttle blade to 1/4 turn open, if I go any more open at all, it develops the lean spike. I'm also running 28 high speed bleeds, 7.5 power valve, and 43 power valve restrictor with 80 jets in the rear to get the power AFR. @12.6:1. The only spot I'm not happy with is the initial shot of fuel, it will go to 12.5:1 on initial shot, that's with orange cam in #1 hole and 31 pump nozzle. I may try and lean that out with red cam, or orange cam with 28 nozzle.

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