1. DARTLARRY

    DARTLARRY Well-Known Member

    Messages:
    503
    Likes Received:
    140
    Joined:
    Mar 19, 2007
    Location:
    FORT WAYNE IN
    Local Time:
    2:33 AM
    I have a 30 over 360 with stock heads, small Edelbrock performer cam, and 625 AFB carburetor. It runs pretty good when driving, but will barely idle, it drops from 750 RPM to 400 when I drop it into gear, and barely stays running. There are some days it runs fine, then sometime during the drive it starts idling bad again. I have changed ignition box, coil, plug wires, distributor, cap and rotor, I have even swapped carburetors, still the same. My initial timing is 20 degrees (that is where it likes it), I think it may be a vacuum leak, but i cant find it, i have blocked every vacuum port on the carb, and sprayed around whole base with water, no change. It is taking a lot of fuel to run, my idle mixture screws are almost all out, and when i partially choke it, it seems to run a little better. I am about to change intakes and see if that helps, any suggestion are appreciated.
     
  2. K.O. SWINGER

    K.O. SWINGER Well-Known Member

    Messages:
    1,489
    Likes Received:
    845
    Joined:
    Nov 18, 2010
    Location:
    oregon
    Local Time:
    1:33 AM
    First thing I would probably do is check timing with a vacuum gauge, manifold vacuum to see if your timing mark is accurate or close. If that shows no improvement I would take the top off the carburetor and check float level when holding the top of the carburetor upside down float should be at a 90°, not sagging one way or the other, at that time I would also check for any contaminants and that all parts are moving freely. That's a couple of ideas. Good luck
     
    • Agree Agree x 1
    • Dubob

      Dubob Well-Known Member

      Messages:
      1,297
      Likes Received:
      528
      Joined:
      Oct 28, 2011
      Location:
      Ohio
      Local Time:
      2:33 AM
      Running exhaust manifolds? Have the heat riser butterfly still?
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      I have 340 manifolds, butterfly is removed.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      Timing is accurate, it just like a lot of timing. I will probably take carb apart and look at it next. it has to be getting all this air from somewhere, but i cant find it. This is crazy once it is past 1500 RPM it is runs great.
       
    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

      Messages:
      27,132
      Likes Received:
      23357
      Joined:
      Jun 19, 2015
      Location:
      Central Washington
      Local Time:
      11:33 PM

      Where IS the timing...initial and total?
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      Initial is 20, no vacum advance, total is 38
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

      Messages:
      19,915
      Likes Received:
      7552
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      Local Time:
      1:33 AM
      Well I can see your problem from here, and it's not the carb. Well it is, but not for the reason you think.
      Since YR started it,lol, I'll let him finish it
       
    • crackedback

      crackedback FABO Gold Member FABO Gold Member

      Messages:
      18,831
      Likes Received:
      3237
      Joined:
      Aug 7, 2005
      Location:
      92201
      Local Time:
      11:33 PM
      350 rpm drop is huge. See if you can check timing at 700 and in gear at 400. If it's consistent at 20*, look for a vacuum leak somewhere. Power Brake boosters are notorious for leaking. Isolate the intake tract, blocking anything that draws vacuum and see if the drop improves. If it does, hook up one thing at a time and see if it changes.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      manual brakes, I have blocked every vacuum port on the carb. no change.
       
    • crackedback

      crackedback FABO Gold Member FABO Gold Member

      Messages:
      18,831
      Likes Received:
      3237
      Joined:
      Aug 7, 2005
      Location:
      92201
      Local Time:
      11:33 PM
      Check any linkage on the carb for interference with your intake. Plenty of times the smallest interference can lift the corner of the carb where it appears to be tight, but is actually not flat on plane with the gasket/intake.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      Carb is flat to intake, installed new heat dissipating gasket and studs as well.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      could this possibly be a leaky valve?
       
    • Rmoore

      Rmoore Well-Known Member

      Messages:
      499
      Likes Received:
      336
      Joined:
      Nov 14, 2018
      Location:
      Gun Barrel City, Texas
      Local Time:
      1:33 AM
      I’m thinking you have blown intake gaskets !!
       
    • rustycowll69

      rustycowll69 Well-Known Member

      Messages:
      2,348
      Likes Received:
      1101
      Joined:
      Feb 19, 2016
      Location:
      Pacific northwest
      Local Time:
      11:33 PM
      I was thinking the same thing. If you're cruising on the freeway, do you get a dusting of oil on the back of the car? If so, maybe the heads have been milled and the intake doesn't match anymore.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      That may be it, I am running a Weiand stealth right now. I have an Edelbrock performer intake, I was going to try it next.
       
    • Rmoore

      Rmoore Well-Known Member

      Messages:
      499
      Likes Received:
      336
      Joined:
      Nov 14, 2018
      Location:
      Gun Barrel City, Texas
      Local Time:
      1:33 AM

      Sounds like a good plan you have there ! I think your going to find the intake gasket will be blown on the bottom of the port most likely !!
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      I figured that what it was, i was just seeing if someone else had any suggestion. Is the Performer manifold as good as the stealth?
       
    • Rmoore

      Rmoore Well-Known Member

      Messages:
      499
      Likes Received:
      336
      Joined:
      Nov 14, 2018
      Location:
      Gun Barrel City, Texas
      Local Time:
      1:33 AM
      As far as I know the eddy is a better manifold ! Someone else may have a different opinion ! Hard to go wrong with the eddy !
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

      Messages:
      19,915
      Likes Received:
      7552
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      Local Time:
      1:33 AM
      proving a vacuum leak into the valley is easy; Just put a vacuum gauge on the dipstick, flip the PCV out of the valve cover and seal the covers, then start her up and rev it up a lil, maybe 1200rpm.Then wait a few seconds
      But I really doubt that's your problem.

      Do not let the pressure rise above 3 or 4 psi, cuz it will want to blow something out, maybe the cam plug in the BH!
      If you don't have a vacuum/ pressure gauge, you can tape over the hole where the PCV was. If the pressure blows it off, yur good to go. If the tape gets sucked in, that's bad.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      I will try that today.
       
    • RustyRatRod

      RustyRatRod Lemmie see your b00bs. FABO Gold Member

      Messages:
      67,580
      Likes Received:
      41743
      Joined:
      Jun 7, 2010
      Location:
      Georgia
      Local Time:
      2:33 AM
      Double and triple check the firing order. I've seen 5&7 get crossed up and not pop at all but idle rough as a cob. 1 8 4 3 6 5 7 2 clockwise.
       
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      I believe the are okay, but will check as well.
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

      Messages:
      19,915
      Likes Received:
      7552
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      Local Time:
      1:33 AM
      When all else fails; Try this;
      Step 1
      crank the rpm up to 1200
      reset the mixture screws to 1.75 turns,
      and then BACK THE TIMING UP, to in the range of 8 to 12 degrees.
      Finally, reset your idlespeed to 650 in gear, and reset the mixture screws to lean best idle plus 1/4 turn, which should be ~1.75 turns.
      If it's not in the range of 1.75 to 2.5 turns,
      then the transfers are still not right.
      If the mixture screws are at less than 1.75 turns, the engine wants LESS transfer fuel.
      If they are at more than 2.5 turns, then the engine wants MORE transfer fuel.
      Do what you gotta do to get the mixture screws into the range of 1.75 to 2.5 at about 700 in Neutral/Park. I'd shoot for 2.25 turns on that AFB
      Step 2
      To set the idle speed, you use idle-timing. Do not be overly concerned about the actual idle-timing number, just give the engine whatever it wants to satisfy the idle speed, and freedom from either stalling going into gear, or banging hard. The less timing she has, and to a point, the slower she idles; the smoother and with less drama, she will engage a gear.

      When the ratio of transfer fuel to idle-mixture screw fuel is right; your engine will, or should, idle just fine, down to 5* idle timing and 550 rpm. I know this because mine does, and it is nearly the same build as yours, except I have Edelbrock heads.

      Step 3
      Tip-in hesitation; you will know you are getting very close to the right ratio of transfer to mixture fuel, because at a slow rate of throttle tip-in, this does not result in a hesitation, and you might be able to reduce your pumpshot; then you know that you are very close.

      Step 4
      you will have to re-engineer the POWER-timing and the RATE of advance to regain the lost response due to the retarded Idle-timing.
      Your biggest hurdle will be to give the engine just the right amount of advance at stall; and then to ramp it up to all-in at the lowest rpm your engine will take it without detonating. Lemmee suggest 34* at 3400 for a safe starting number. Whatever the timing turns out to be between idle and stall is of very little consequence because you can augment that with Vacuum-advance timing; oh sorry, your D does not have a V-can/your loss. IMO, you need to fix that.

      OK here's the theory;
      At 20* idle-advance you have basically nearly shut off the fuel supply from the transfers, and are idling almost exclusively on the mixture screws. Then when you put it into gear, the engine cannot get enough fuel under load to continue running at the chosen idle speed.

      Go back to post #1 and revue what you wrote
      This here is telling me the engine wants more transfer fuel. The only way to do that is to increase the throttle opening.... which increases the idle speed ....... which makes it slam into gear harder. Your only other choice for idlespeed control is to reduce the idle-timing. This is why I said "I can see your problem from here".
      BTW
      That "small" Edelbrock cam works best with headers to wake your bottom-end up.

      My apologies to @yellow rose for jumping in, but this thread was IMO, rapidly decaying.
       
      Last edited: Nov 23, 2020
    • DARTLARRY

      DARTLARRY Well-Known Member

      Messages:
      503
      Likes Received:
      140
      Joined:
      Mar 19, 2007
      Location:
      FORT WAYNE IN
      Local Time:
      2:33 AM
      Thank you, that makes real good sense, I will try that tonight. I had headers on it, but got tired of fighting them to work on anything underneath. That is why I put the manifolds on, they quieted it down, and made it easier to work on.
       
    1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
      By continuing to use this site, you are consenting to our use of cookies.