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Hot Rods Jetting dual holley carbs

Discussion in 'The Hokey Ass Message Board' started by TooManyFords, Oct 30, 2016.

  1. TooManyFords
    Joined: May 21, 2008
    Posts: 553

    TooManyFords
    Member
    from Peotone IL

    Looking for so help. I have a 4 Galaxie with a 390 with 406 heads and a 63 dual quad manifold. Several years ago i installed this engine replacing a 352. At the time i installed 2 Holley 450 carbs. I did not know what they were when I bought them. After research I find they are better suited for a high winding small block with a tunnel ram and big gear. I have none of that. Car is a cruiser and yes I know it would run better with one carb but i like the look of two. With 450s it stumbled on take off real bad due to manual secondarys opening and not enough rpm. Other that that it ran OK and pulled down 15 mpg. I perched a matched set of 600s (naby years ago for a 428) and yes I know these are too bid although a buddy ran 2 600s on his 390 with no issues. I am not making a race car it is a driver. I just trying to get the jets close. Since r9834ebuilding the carbs and on its first road test about 3 miles it ran terrible, worse than 450s. 450s were jetted 20 sizes bigger than the 600s. 65s in the 9834s and 85s in the 450s. With the 600s it was backing firing out the exhuast at steady 55 cruise. I am sure the power valves need replaced. have 6.5 with 8 inches of idle. I would like to knock down the tear down time on jet replacement due to having to pull one carb each time for jet swap. Ok that was a lot of information and probably not nough. Help.Oh and it is a stock auto trans with 3.00 rear gear.
     
  2. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 1,355

    19Eddy30
    Member
    from VA

    There is more going on then just a jet change , power val, squirter's , squirter cams , emersal tubes , air bleeds and so on ,
    You're going to have to experiment and keep notes of everything you do,, I would start off by buying yourself a good vac gauge & a Wide band O2 gauge , It can be removed later , & if you're using gas with ethanol ,you will be unable to read spark plugs like the old days , even with pump gas without ethanol
    This will help http://members.tccoa.com/392bird/tuning.htm
     
    wedjim and mad mikey like this.
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 50,202

    squirrel
    Member

    first thing to do is to find the Holley info for the list number carbs you have, and put the stock parts back in them...stock jets, etc.

    some folks seem to think that carbs need to be jetted differently for different size engines. That's generally not the case. The carb doesn't care about how big the engine is, it just needs to mix the right amount of fuel with the air that is passing through it. That ratio does not change with engine displacement.
     
    wedjim and 46international like this.
  4. are the 600s vac secondaries? sounds like the 450s are not. I think you would need vac secondaries for a big car like that.
     

  5. TooManyFords
    Joined: May 21, 2008
    Posts: 553

    TooManyFords
    Member
    from Peotone IL

    Carb is back to stock jets. Yes I went with vacuum secondaries this time. I think it is lean.
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 50,202

    squirrel
    Member

    If you want it to run right, take off the dual quad intake and put on a single carb.

    In the mean time...where is the ignition timing set? what does it do as RPM increases? Have you confirmed that the rest of the engine is in good condition? Float levels set right? What condition are the carbs, are they new? or rebuilt? if rebuilt, by whom?

    also what dash number are the carbs? (9834-2 or something? or just plain no dash?) The holley book shows 68 primary jets
     
  7. TooManyFords
    Joined: May 21, 2008
    Posts: 553

    TooManyFords
    Member
    from Peotone IL

    9834 no dash fresh by me with Holley kits, Yes I have done dozens of Holley carbs in my lifetime. No it is not going back to one carb. Base timing is 14 and total is 32. It has been upgraded to Dura Spark. Engine was rebuilt by a race shop before i bought it with 10k miles on it. Cam is a comp cams 268h.
     
    loudbang likes this.
  8. wedjim
    Joined: Jan 1, 2014
    Posts: 420

    wedjim
    Member
    from Kissimmee

    I would be surprised if it's lean at cruise with two 600 Holley carbs. More likely it's rich.
    I'd try a wide band O2 system in the exhaust for tuning, as well as a vacuum gauge to see what it doing going down the road in both areas.

    Maybe progressive linkage if the manifold plenum will allow it to fuel all cylinders that way on 2 barrels?


    Sent from my iPad using The H.A.M.B. mobile app
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 50,202

    squirrel
    Member

    ...or a block off plate under the front carb....????
     
  10. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    I deleted my posts and sent you a pm. You are being fed a steaming crock of shit here.
     
  11. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 1,355

    19Eddy30
    Member
    from VA

    You can install pretty much what ever carb's you want & it will Run,
    But do they run correct From idle , cruise, to full throttle ?
    there a lot to do if you want the correct fuel / air delivery ,it take work & understanding
    notes trial and error , also there more then the the Carbs , The Timing ,spark plugs , timing curve & more then this . I have a Flatty with 2 carbs, I have spent over 40 hrs until I had them tuned correct for that Engine combination, I all so run a tunnel ram with 2 550's two barrels full out race motor on street , Tme , Time & Time has went ito this set up HAPPY with the results , but there is still a little more to gain , it runs 6:70's on street & track 1/8 mile SBC , NO N.O.S , NO BLOWER ,NO TURBO ( & detuned) with a 30 inch tall , 7 wide tire with a 3:40 somting gear , I think it's a3:43 to May car's combination (all steel, full fender, none chop A , NO big tire or slick ) street tire Bridgestone
    I will be installing a pair of Holley Ultra HP carbs because they are 100% complete ajustable no more drilling fixing holes everything screws out ,

    Go back to the original OP ,,
    It's all about CFM's , Air /fuel Ratio From Idle to wide open !!!
    Not just a bolt on , every Engine is different
    This why so many are going to electronic fuel injection , they do not want to put the time Work into tunning & learning carb's!!
    Tools I use is a 6 inch vac gauge that read's in 1/4 pd increments from 0-30
    A Good Quality wide band O2 gauge
    Auto meter 5 inch tack ( that I can remove )
    Go Pro to record all three at same time
    BUT I AM ANEL ABOUT TUNNING ,
     
    Last edited: Oct 30, 2016
    falcongeorge likes this.
  12. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,255

    jimmy six
    ALLIANCE MEMBER

    I've found the stock jetting to be fine in most cases, like said above its fuel to air ratio that you are working with. With that said; if your compression is higher than stock you normally add some bigger jets until the plugs read correct. Same for an ignition. A hotter ignition can stand a wider gap which in turn can burn more fuel= bigger than stock jet= more power. I've found most power valves are too high for me ive taken out 106's and installed 55's or 65's. Good luck.
     
  13. Just to ad that those 450's come stock with 58 jets, whoever put 85's in were really searching, on my 383 sbc my best combo was a 61 in front carb and 63 in rear carb. Like 19Eddy30 said it takes time to get any carb right but paying due diligence never ceases to provide results.
     

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