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Hot Rods 6x2 sbc carb issues

Discussion in 'The Hokey Ass Message Board' started by Drivinford, Dec 14, 2019.

  1. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    I have this edelbrock 6x2 setup on my model a, solid linkage, power valves deleted and 53 jets.
    The issue I'm having is when I punch the gas down sometimes I get a back fire out of a carb and a puff of black smoke out of the headers, once that's out of the way if I stay in the gas she runs strong.
    Any ideas on what to do or check would be greatly appreciated
     
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  2. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,103

    Jmountainjr
    ALLIANCE MEMBER

    What carbs. How many have idle circuits.
     
  3. THE FRENCHTOWN FLYER
    Joined: Jun 6, 2007
    Posts: 3,040

    THE FRENCHTOWN FLYER
    Member
    from FRENCHTOWN

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  4. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
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  5. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
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    They all have idel circuit's
     
  6. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    Is it a lean pop and stumble ? What is the timing at ?
     
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  7. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    That's what I'm trying to figure out, it started off where the plugs were completely black, now there a brownish cold with a little black, when I blocked the power valves I put bigger jets in, and it wouldn't run for nothin, took those jets out and put 53s back in and it ran better but still back fire, it back fires when I'm getting out of the idel circuit, if I tap the gas quick then punch it down the car takes right off now issues, it's when I'm cruising along and or come to a stop and lightly get in the gas, then it back fires
     
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  8. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    Im gonna plug the vac advance and try running without that see where it gets me
     
  9. PackardV8
    Joined: Jun 7, 2007
    Posts: 888

    PackardV8
    Member

    You're a braver man than I am, Gunga Din. I've never, ever had a 6x2 that didn't have a flat spot, a stumble, a bog somewhere in the rev range.

    Your backfire out the carb is as likely to be ignition as fuel. When was the last time you replaced plugs, wires, cap and rotor?

    Bottom line - lookin' cool costs.

    jack vines
     
  10. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    The vacuum advance doesn’t change anything at full throttle .
    What’s the base timing ? Any more details on the engine ?
     
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  11. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
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    Everything is brand new!
     
  12. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    Base timing I've had anywhere from 12 to 16, stock edelbrock e street 350
     
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  13. wicarnut
    Joined: Oct 29, 2009
    Posts: 3,627

    wicarnut
    Member

    I've only known 2 men that have run a 6X2 setup on hot rods, both only used the middle carb on each bank, other 4 were for show and they do look Kool. 6 X 2 without progressive linkage is a race deal IMO and you are probably over carbed for your mild street use engine, again IMO. Lots of variables to play with/adjust to hit the right combination, Good Luck. I never cared much for multiple carb setups, back in my day, had Tri-Carbs, easy to tune, used progressive linkage, various 2X4 deals, never the right combo, and my junk always was faster/better/consistent with one 4 barrel, correct size and tuned for what I had. The multiple setups are mostly for show, again IMO. Check your manifold vacuum, could be the source of backfire problem.
     
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  14. Hemi Joel
    Joined: May 4, 2007
    Posts: 821

    Hemi Joel
    Member
    from Minnesota

    It sounds like maybe it is getting too much pump shot, with the puff of black smoke. I would slow down the accelerator pump shot, or switch to a progressive linkage. I use a progressive linkage on my 8 carb Hemi, with the center 4 opening about 1/2 way before the outer 4 even start. Also, I have no idle circuits on the outer 4. It runs great on the street and drag strip. hemi coupe on road cropped.jpg
     
  15. jimmy bruns
    Joined: Jun 21, 2011
    Posts: 70

    jimmy bruns
    Member
    from Chatsworth

    I'd ditch the straight linkage and pick up a progressive.. i run all 6 on my 324 olds with 97's has no issue runs on 2 until i really get on it. Also should try a new set of plugs maybe a hotter plug and a timing adjustment should do the trick. Not sure what a stock jet is for a 94 but i went with stock jets, and power valve in the 97's and have had zero issues as my daily driver.
     

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  16. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,103

    Jmountainjr
    ALLIANCE MEMBER

    It's a process. The accelerator pump arm has three holes that control the pump. Start with all set at the inboard hole to get less shot. If you then need more, start by adjusting the center two carbs. I would consider running power valves in the two center cards. Make sure that the power valves and block off plugs are machined for 94s. New Holley PVs don't fit tight and will drip by the threads. You might also bump up the jets in the center two carbs by two sizes. I usually start with the linkage off, close the end carbs idle screws and back off the idle speed screws on the end carbs. I try to get idle speed and mixture on the center two carbs and then balance with the end carbs if needed. An AFR gauge will be your friend. Then hook the linkage up without disturbing the carbs throttle arm positions. Drive. Adjust. Repeat. Maybe many times. The biggest issue is getting enough air velocity through the carbs so that they will meter correctly. Depending on your intake design you might need carb spacers. Sometimes they help. And a cam with decent idle vac numbers.
     
    Last edited: Dec 15, 2019
  17. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    Thanks alot man!
     
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  18. 51box
    Joined: Aug 31, 2005
    Posts: 885

    51box
    Member
    from MA

    Put power valves back in it. If you are running straight linkage the carbs need to function as original. You might need ones that actuate at a lower number but it will run properly with them.
     
  19. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    What will I gain putting the power valves back in? Thanks!
     
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  20. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,103

    Jmountainjr
    ALLIANCE MEMBER

    Added fuel enrichment under conditions of low manifold vac tuned by the vac rating of the power valve. If you are going to be playing with a 6x2 you will need to have a good understanding of carb function as that setup is not a bolt on set it and forget it kind of thing. That's why so many are running around dummied up.
     
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  21. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 912

    Elcohaulic
    Member

    I would remove the vacuum advance and try running straight timing and see what that does.. If it cleans it up try working from there.. Maybe more initial with less advance or just run straight timing. I've done that on street engines for hundreds of thousands of miles...

    When I get into carbs plural, the vacuum advance is usually the first thing to go..
     
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  22. Stock 94 jets are 51. Putting power valves back in an engine that has a backfire condition is making more work for you. 2X^ double check those power valve block offs, sounds like one may be leaking vacuum causing the backfire. I would change to 50's or 51's and reset the accelerator linkage 2X^.
    Plus use only two carbs for idle. The other 4 should have the idle screws bottomed out AND the throttle plates adjusted to be fully closed at idle. BUT only make one change at a time...just like on a race car. Small plenum, long ports you can use a lot of carb......big plenum and short ports for racing, use very tiny carbs on the street, 450's or 390's 2x4 or original Holley / Ford 94's. Your mechanical advance needs to be in by 2500 rpm. The vacuum advance is an option if the mechanical is working right.
     
  23. gasshole
    Joined: Oct 1, 2006
    Posts: 329

    gasshole
    Member
    from new jersey

    it will be easier to tune with more initial timing. crank it up to 30 at idle and try that. if it helps go back ant limit mechanical timing in the distributor.
     
  24. 51box
    Joined: Aug 31, 2005
    Posts: 885

    51box
    Member
    from MA

    I run 6x2 straight linkage on my car. 12 initial and 32 all in by 2,500. Mechanical advance. All carbs function as original.
    Progressive linkage is designed to be used with primary and secondary carburetors ie no idle circuits. Turning in idle screws is not the same as not having an idle circuit.
    There is nothing easy about running six carbs direct on the street but it can be done and run properly without belching smoke and stumbling.
     
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  25. jaracer
    Joined: Oct 4, 2008
    Posts: 325

    jaracer
    Member

    Initial acceleration with opening all 6 carbs at once is a delicate balancing act. I would suggest you get a uni-sync tool and make sure each carb is passing the same amount of air at idle so they are synchronized. That should be your starting point. Motorcycle mechanics synchronize multiple carbs all the time. A friend, and motorcycle guy, cured a poor accelerating Astin Martin by using his uni-sync tool and setting all the webers the same. Flat spots went away.
     
  26. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    Would I be better off replacing this distributor with a mechanical advance and get rid of the vac? I'm gonna be putting .50 jets in for starters, I wonder if closing the outer 4 carbs idle circuits off will lean those cylinders out?
    Thanks alot guys!
     
  27. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

  28. dana barlow
    Joined: May 30, 2006
    Posts: 3,888

    dana barlow
    Member
    from Miami Fla.
    1. Y-blocks

    Vac. canbe locked up.,if you have distributor that also has mec. advan. built in. If it has no mec advan.,you need one that dose. Vac. adv. with 3 or more carb.s is not a working thing for the most part.
     
  29. Drivinford
    Joined: Aug 24, 2012
    Posts: 706

    Drivinford
    Member

    I put size 50 jets in, along with a new coil and distributor. One of my issues might be the vac advance I drilled into the carb, see the pics below, I'm getting fuel in the vac line which might be causing some of my issues?? When I took the car for a spin a little bit ago, I was getting into the throttle and a puff of smoke? was coming out of the carb, it would run decent up until I pushed the gas down, it hesitates and puffs out of 20191224_163927.jpg 20191224_163926.jpg the carb
     
  30. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,103

    Jmountainjr
    ALLIANCE MEMBER

    I am not saying if you should, or should not, be using the vac advance. I personally don't. But if you do, you can decide if you want manifold vac or ported vac off the carb. The vac port on the carb is the brass plug above and to the right of where you drilled the carb. It's 3/8-24 straight thread.
     
    Last edited: Dec 24, 2019

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