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Thread: 4150 Over Fueling

  1. #1

    Default 4150 Over Fueling

    Hello. I have a Holley 4150 (list 3043, 386315006) on a Chevy 327 engine which runs very well. One of the bolt holes in the main body had gone bad, and I swapped the main body with a body of a 4160 (list 3005, 1743). I used also the primary metering block of the 4160 (with both primary jets and power valve of the old 4150 installed), and all other parts remaining from the original 4150. Started up; getting too much fuel through the discharge nozzles and the booster venturis. You can see the fuel literally flow into the engine, and the engine will stop after about 20 seconds cause of over fueling. Can only keep it running by increasing the idle speed.

    I checked:
    1. The float level: it is ok, as there is no fuel coming out of the sight plug of the primary fuel bowl.
    2. Needle and seats: are ok, new.
    3. The fuel pressure: its 5 psi which is also fine.
    4. The floats: tested, they are not leaking (they shouldn't as it was running fine with the bad main body).
    5. The power valve and its gasket: no leaks.
    6. The accelerator pump diaphragm: no leaks.
    7. The idle air bleed jets: open.
    8. Gaskets: ok and not covering any holes inside the main body/metering block.
    9. The choke valve: working correctly.

    No improvement. I did check out the forum's archive, but nothing which I already didn't try. Any ideas?

    Best regards, Joep

  2. #2

    Default

    Need a little bit more info as to where the fuel is coming from during startup that you say is "too much fuel through the discharge nozzles and booster venturis".

    I'll address both situations.

    Discharge nozzle should not be leaking any fuel at idle or motor off condition. If so, then it is missing the check ball valve assembly under the nozzle or the check valve assembly is not doing its job. Fuel should only discharge while moving throttle linkage.

    The booster, in the middle of the venturis, should also not be leaking any fuel during an idle or engine off condition. The booster should not begin to flow till about 1800-2000 rpm. If the booster is dripping at idle or engine off condition, then either the fuel level is to high in the bowl, or there is trash in the needle seat not allowing fuel flow to stop.

  3. #3
    Join Date
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    Ont. Canada
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    Default

    Quote Originally Posted by 69cam View Post
    Need a little bit more info as to where the fuel is coming from during startup that you say is "too much fuel through the discharge nozzles and booster venturis".

    I'll address both situations.

    Discharge nozzle should not be leaking any fuel at idle or motor off condition. If so, then it is missing the check ball valve assembly under the nozzle or the check valve assembly is not doing its job. Fuel should only discharge while moving throttle linkage.

    The booster, in the middle of the venturis, should also not be leaking any fuel during an idle or engine off condition. The booster should not begin to flow till about 1800-2000 rpm. If the booster is dripping at idle or engine off condition, then either the fuel level is to high in the bowl, or there is trash in the needle seat not allowing fuel flow to stop.
    Or the high speed air bleeds are too small or plugged.

  4. #4

    Default

    Thanks for the suggestions. I mean both primary boosters which are leaking (flowing) at idle. The strange thing is that the fuel level in the bowl isn't too high, as there is no fuel coming out of the sight plug when removed. This why I exclude the needle & seat assembly or fuel level in the bowl as causing the trouble. Moreover, the boosters are not dripping when the engine is off.

    High speed air bleeds sizes are fixed and identical to the original main body. I blew them out with compressed air and all of them are open.


    Any more thoughts? Joep

  5. #5

    Default

    OK that makes a little bit more sense. So I'm assuming you used the float bowls from the 4150? I would compare bowls from the respect of float bowl plug inspection hole height difference. Something is telling me that the metering blocks from the 4160 don't have the same fuel level height requirements as the 4150's do. We can try a couple of things to try and pin point whats going on.

    Just to see if the booster will stop dripping, lower the fuel level on both primary & secondary bowls. Lower it quite a bit. DO NOT DRIVE THE VEHICLE. I just want to see if the boosters will stop dripping at idle. Start the car and check the boosters. If after lowering the fuel level in the bowls quite a bit, and it still leaks then you have a needle & seat issue. If it stops leaking then you have a difference of float bowls between the 4150 & 4160 from respect of the metering block and how much fuel they will tolerate before it starts dripping through the boosters. I suspect the reason the boosters are not dripping when the car is off is that you have a mechanical fuel pump. If you have an electrical fuel pump and you just turn your pump on I would suspect the boosters are dripping. In your case I wouldn't automatically suspect a problem with needle and seat due to a possible issue with float bowls/metering blocks. If you do have an electrical fuel pump you should be able to test without have to start the vehicle. Just turn the pump on to check each situation.

    I loaded some pics to help understand how fuel flow starts from the float bowl to the actual booster. Fuel enters the carb directly from the main jets into the main wells. You can see from the clear metering block how it branches off from there. Fuel level needs to be pretty high to flow out of the boosters. I personally had this problem about 1 year ago. I ended up having some trash right on top of my needle assembly so the float assembly never could meter fuel properly and it would just fill the bowls up and drip like crazy out of the boosters.

    In the pic you can see passage number 7 is the passage the flows directly to the boosters:

    Click image for larger version. 

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    Click image for larger version. 

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  6. #6

    Default

    Thanks again for trying to help me out. Regrettably, no luck so far. The primary fuel bowls of the 4150 and 4160 are identical with identical sight hole heights. The sight hole in the secondary fuel bowl is a little lower indeed. But this is again the same for the 4150 and 4160.

    I do indeed have a mechanical fuel pump. I tested the needle and seat assembly with compressed air. No leaks. Also the fuel level in the bowl is never rising above the sight holes, so I suppose the fuel level is correct and the needle and seat assembly are working as they should. Besides that I tried all possible swaps with the 4150 and 4160 fuel bowls and metering blocks. No difference.So I am afraid we have to look for the problem in the main body.

    The air bleed nozzles are all blown through with compressed air and open.

    What I did notice however today, when I compared the new main body with the old one, is that both holes on the underside of the main body which are connected with the hole mentioned "curb idle discharge" (3) in your picture have been plugged off. Instead a hole has been drilled (left and right side),through the main body right into the barrel (L+R) just above the throttle valve. Is this a common tuning trick or might this be the cause of the trouble?

    Thanks for your thoughts, Joep
    Last edited by feldmann; 07-23-2015 at 06:02 AM.

  7. #7

    Default

    I tested the needle and seat assembly with compressed air.
    Not sure what this accomplishes, but it's not an accurate test of testing the needle & seat. To test your needle & seat, lower the fuel level below plug or site glass. Start the motor, let it idle. Is the fuel level rising in the site glass or leaking out of the plug? If so, needle & seat is bad.

    Also the fuel level in the bowl is never rising above the sight holes.
    You're checking this with the engine running correct?

    Instead a hole has been drilled (left and right side),through the main body right into the barrel (L+R) just above the throttle valve
    Is this hole where it is leaking at?

    If your 100% sure your needle & seat are working and your air bleed passages are not clogged, then you have some sort of problem with your main body or metering blocks. If someone drilled some holes through the main body I would suspect that would be your problem.
    Last edited by 69cam; 07-23-2015 at 10:03 AM.

  8. #8

    Default

    There is no fuel coming out of the sight holes. I checked that indeed with a running engine. That's why I rule out the needle & seat.
    It's flowing through the boosters when running. The engine dies shortly after starting because of this.

  9. #9

    Default

    Quote Originally Posted by feldmann View Post
    There is no fuel coming out of the sight holes. I checked that indeed with a running engine. That's why I rule out the needle & seat.
    It's flowing through the boosters when running. The engine dies shortly after starting because of this.
    Alright, my last thought is a little backwards, but I think it could work. Take the carb off the motor. I would stuff the venturi with a rag from the bottom side of the carb. On second thought, I would put some plastic in first back by a rag right up close to the bottom of the booster. Make it a pretty tight fit. Use your bowl bolts and stack a bunch of washers, or find some shorter length bolts. Put the metering block on with gasket. Now with the venturi you stuffed the plastic backed by a rag, and fill it with gas till it submerges the booster. Let's see where the gas comes out from on the metering block. You might need to try this both ways. Once with the metering block on the body, and once with out it. Let's see how the booster is getting fuel through it. With the booster being so high on the body, gas has to be "pumped" up there for it be coming out at idle. I'm thinking there has to be something wrong with that carb body, for gas to be coming out of the booster at IDLE, and the fuel level in the bowls, not over the site glass/plug. You might wanna try getting some small wire to push through the air bleeds. You can strip some 12-14 AWG stranded electrical wire to get the right size.

    The hole on the booster itself, is very small. You might could try WD-40 with the red nozzle right over the hole, and see if you can trace back where the fuel is coming. If not, try any variation of the above method. Just trying to seal the venturi just below the booster so you can flood the booster to back trace how the fuel is getting to the booster other then its normal path.

    Did some digging around to try and find a better diagram to show you how a booster gets fuel. Fuel "normally" is not pumped out a booster. Fuel is normally sucked out of the main well that the booster is connected to. It's essentially a vacuum affect (negative pressure). Once you get enough air flowing through the venturis (1800 rpm or so), it will pull/suck the fuel through the boosters.

    Click image for larger version. 

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    Hope that helps.
    Last edited by 69cam; 07-24-2015 at 10:04 AM.

  10. #10
    Join Date
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    Default

    Fuel will come out the boosters at idle if the high speed air bleeds are plugged or too small. Some metering blocks have a kill bleed in them to slow the booster down.
    Your problem is on the air bleed side. What was the problem with the original main body? If it was a stripped thread you can put a Heli-Coil in, and use the original main body.

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