Engine Carb Issue? Looking For Some Suggestions Guys.

Discussion in 'Fox 5.0 Mustang Tech' started by dsinka01, Apr 27, 2014.

  1. Ok , Im going to throw some information out there, some relevent and some probably not so relevent , so that we can all get a better picture of what's going on.

    I have a 351W stuffed into my fox. I have an edelbrock intake, with an edelbrock 1406 carb with an electric choke, and the msd 6al ignition box, with matching Msd distributor( doesnt have vacuum advance). This car is supplied fuel by an external fuel pump, pumping fuel through a -6an braided fuel line, to a holley fuel regulator, which i have set at about 5.5 psi to the carb. The carb is sitting on a 1 inch spacer.

    The problem(s) i am having are that
    1. It takes holding the gas pedal to the floor to start it, then i have to hold the gas pedal to about 2000 rpms for a couple minutes so that i can finally get it to idle. Once it comes to an idle, it will continue to idle just fine. I can even rev it up, and have no bogging down issues or anything. regulator stays at a good 5.5 psi.

    2. When i start to drive , climing up 1st gear and into second it'll hesitate pretty bad to the point of stalling out if i dont ease up slowly.

    3. I finally work my way up to cruising speed, everything seems fine, until i try to let off the gas to downshift, or sometimes let it into neutral to coast to a stop sign...it'll flat out stall on me...but it starts right back up. or while im cruising and i let off the gas a little bit it stalls, but i can start it up while coasting.

    Im up for any suggestion.. I'm a computer tech by day, and a wannabe car guy by night..this is all new to me, so there is VERY easily a chance im missing something simple.

    The timing is set the way MSD suggests with the base timing and the whole advanced timing (cant remember the degrees )

    The carb was a refurbished carb i got online from "the carb guy" out of texas...and he says it's set to boltup and go.. which he seems to know his stuff so wont question that.

    I have a fuel filter screen on the end of the pickup in the fuel tank, i have one before the fuel pump, and i have one just before the carb, so i think the fuel is pretty clean. I pulled off the top of the carb because i had to readjust my floats, i didnt always have the fuel regulator on it, so it was pumping way too much fuel and it bent the float out of adjustment. ( or so i think.) I did set them as to what edelbrock suggests.

    whew this is long winded.

    so guys what can i try? what can i look for? how can i go about troubleshooting this issue?

    Thanks in advance ,

    wannabe car guy (derek)
  2. Derek, your background matches mine, except for age and experience. Good computer techs that know hardware and electronics can figure out almost anything...

    Let's look at this and see if there are some things missing.
    EFI to carb swaps are notorious for poor quality work and shortcuts that are poorly done and in some case downright dangerous.

    The computer should not be left in place to control the ignition timing advance. If it is, you have gotten a bad deal. There are no sensors to tell the computer how much spark advance is needed. Therefore you have no spark advance that is needed for best performance.

    Carb engines need a distributor with mechanical advance or built in electronic advance. You can check for the presence of a working mechanical advance by removing the distributor cap and trying to twist the distributor rotor both directions. It should move a significant amount in one direction. No movement means the distributor has an electronic advance or no advance at all. Check the manufacturer's part or model number against what you find on Google to determine what type of distributor you have.

    Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. The EFI pump puts out 40+ PSI and is designed to pump pressure more than volume. If the add on pressure regulator fails, you will flood the engine with gas and wash all the oil off the cylinder walls. That will cost you big time $$$. Some people will attempt to leave the EFI computer in place in an attempt to control either the electric fuel pump or ignition. This is a sure sign of ignorance and poor quality workmanship.

    Here's a link to the carb owner' manual. You may already have it, but just in case you don't, here it is.
    I suggest that you download the manual and take some time to read it cover to cover. Once you understand how the individual systems or functional blocks work in a carb, troubleshooting becomes much easier.

    1.)The first step is to check the vacuum plumbing and make sure there are no leaks or broken lines.

    2.) The no idle when it is cold is a symptom that the electric choke isn't working like it should. Take off the air cleaner and see if the choke butterfly closes when you step on the accelerator on a cold engine start.

    3). Page 6 of the owner's manual gives some instruction on how the carb enriches the air fuel mixture. It uses intake manifold vacuum, so make sure all the external vacuum lines are in good shape. The actual vacuum used for the metering rod control is internal to the carb. Look closely at the carb base to make sure the intake manifold gasket doesn't cover up the vacuum port for the carb's internal vacuum system. Most likely the vacuum is picked up just below the primary throttle butterfly, but it might be using a different source for vacuum.

    4.) While the air cleaner is off, watch the primary throttle bores and quickly move the accelerator linkage by hand. You should see a squirt of fuel in both primary throttle bores. If not, or it's weak, that would account for the poor acceleration.

    5.) This carb is similar in function to the old Rochester Quadra Jet, which most mechanics hated. It is an Air Valve carb and airflow operates the carb's secondary systems and mixture control. Make sure the secondary airflow butterfly opens and closes easily and smoothly.

    See https://www.google.com/webhp?sourceid=navclient&ie=UTF-8#q=edelbrock+1406+carb+tuning for more help and even some YouTube videos
  3. Yep, I bet that covers it. I would not be surprised if the choke is too tight and needs the unloader tab to open up a bit and start. If the Edelb. carb has idle mix screws (it must) and it must also have a throttle stop screw, you will be adjusting them. No computer controlled air bypass circuit or tps required here.
  4. As soon as I read edelbrock carb I didn't have to read much further... I have zero luck with them carter/afb want to be carbs what so ever!