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Thread: 4150 Over Fueling

  1. #11


    OK, a little update.

    I did the test suggested by 69cam. I squirted WD-40 through the boosters, and this was coming out only from the main jets, which looks OK to me. Also I did blow out once more the air bleeds, to exclude the problem suggested by 81TransAm. No improvement. However, still too much fuel out of boosters, with fuel level below the sight holes in the primary float chamber.

    Afterwards, I repaired the old main body with a Heli-Coil. Put everything together, and surprise: same problem. Too much fuel out of primary boosters.
    Though I didn't change the engine settings, I now suspect that there is a vacuum, or ignition problem, or probably something else. What do you say?

  2. #12


    Hmm, so from the last picture I posted, and by your test results, you can see that fuel gets to the booster from the main well, which is fed from the main jets, which is fed from the float bowl. As I've stated before, fuel does not normally flow through the booster at idle. Not enough airflow at idle to create enough negative pressure, to cause fuel to flow to booster. In your case, it's quite the opposite. Fuel is flowing at idle. So, pull power from the distributor so the car won't start. Turn the car over in 5-6 second attempts. Is fuel flowing through booster while cranking? Have the boosters been tampered with?

    I'm not trying to be captain OBVIOUS here but fluid will find it's "LEVEL". So if your fuel is at X height in the bowl, it will also be at x height in the main well. When you look at the last pic I posted. Fuel levels out in the main well. For it to come out the booster, it has to go up hill. HOW IS FUEL GOING UPHILL AT IDLE?

    This is why it requires enough negative pressure to pull the fuel up and the high speed air bleed helps it out by metering air into the stream as well.

    Do you have an air compressor? If so try taking the air nozzle and with the engine off start blowing air over the booster venturi like it would if the car was running. Did fuel start dripping out of the booster? If so, when you stop blowing air does the booster continue to drip? trying to see if you got some kind of siphon affect going on. When the negative pressure no longer over comes atmospheric pressure the booster should stop flowing. Im wondering if the emulsion holes or kill bleed is blocked if it would create some kind of siphon affect. For you to be dripping fuel at idle something has to be pushing fuel. Idle air flow is not enough to pull it out.

    Here is quick video of a booster in action. You can see the delay it takes to get a booster to start flowing: Watch the end. Real good slow motion video.
    Last edited by 69cam; 07-29-2015 at 02:01 PM.

  3. #13


    Thanks, appreciate that you try to help me.

    When I crank the engine with the coil detached, there is no fuel coming out of the boosters. I will check the compressor test tomorrow. There haven't been any fiddling with the boosters.

    I have a Duntov cam on a 327 SHP engine which will normally idle (rough)at around 1000 rpm. Probably I need to check the ignition or something else, which causes the engine require higher idle, which causes in its turn the drawing in of fuel through the boosters? Just another thought. What do you think?
    Last edited by feldmann; 07-29-2015 at 03:58 PM.

  4. #14


    I'll see if the compressor test works. With air above the venturi, the booster starts spraying fuel. Without air, it stops. Spark plugs are all black & wet from too much fuel.

  5. #15


    Quote Originally Posted by feldmann View Post
    I'll see if the compressor test works. With air above the venturi, the booster starts spraying fuel. Without air, it stops. Spark plugs are all black & wet from too much fuel.
    If your gonna see if the compressor test works, then how are you already able to provide results of said test?
    If that is case, it appears to be working properly. Are you high idling? 1500-2000 RPM.

    Is your carburetor sitting level?

    I have laid everything out that shows how fuel gets to the booster, and the related issues that would cause problems.
    None of the issues seem to affect you yet your carb continues to be dripping fuel at the booster.

    Anyway you can post of video on YouTube and link it here? Even if it's just a cell phone video. As long as we can hear & see what's going on.
    Last edited by 69cam; 07-30-2015 at 11:25 AM.

  6. #16
    Join Date
    Nov 2014
    Ont. Canada


    For fuel to come out of the boosters at idle, one of two things are happening:
    1) Your vent tube is plugged, and the fuel pump is pumping air into the fuel bowl and pushing the fuel out. But you would also see fuel coming out the air bleeds. Since you have not said this is happening, I doubt this is your problem.
    2) You have a blockage in your high speed air bleed circuit. With the HSAB restricted, there is enough air flow at idle to pull fuel out the boosters. That is part of what the HSAB does. It times when the booster starts to flow. If it is restricted or plugged, the booster starts to flow too soon. In this case at idle. Since you said boosters and not booster, I'm going to guess it's happening on both boosters. I would look at you gasket first. Find the HSAB passage and hold the gasket up to the carb, to see if the passage is open. Then hold it up to the metering block, and check to see if it's open.

  7. #17


    Quote Originally Posted by 69cam View Post
    If your gonna see if the compressor test works, then how are you already able to provide results of said test?
    Sorry, mistype. I did the compressor test and it worked as you described.

    Yes, indeed. High idling above 1800 to keep it alive. I took all spark plugs out, some cylinders are full with fuel. Have to try later. Car is level.
    Last edited by feldmann; 07-30-2015 at 01:32 PM.

  8. #18


    OK, I think it's solved. Repaired the old main body with a Heli-Coil, put all parts together, and it still flooded while running. Changed metering block gasket for a better quality one, and tightened the fuel bowl bolts harder, and the problem disappeared. I think I have been too careful with tightening these bolts, cause of the damaged threads before, and that's why fuel went everywhere between the metering block & main body. Thank you both for helping me out!

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