Fuel Carb- Overflow

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Joined
Nov 28, 2014
Messages
119
Reaction score
14
Location
Charlotte
My Car
1973 Mustang Convertible.
Restoring and fixing as I go.
Noticed the odor of fuel when I went to park my car. Also noticed Black Smoke when starting my car. Noticed it's coming from the Carburetor.
I don't know much about carbs (except eating them) . Do i need to adjust the carburetor or does it need a rebuild to address the leaking?
How do I address the leaking?

View attachment 20190620_201903.mp4
 
Most likely the fuel inlet valve (needle and seat) on the one of the float bowls is either stuck open or the o-ring seal on one of the needle and seat cartridges is leaking. They can be replaced with out removing the Carburetor (unless you want to eat it LOL). Remove the fuel level checking plug on both the front and rear carb float bowls and see if the fuel level is even with the bottom of the lower threads with engine running. If fuel pours out of either bowl plug you found the flooding issue.

Ron
 
It could also be a chunk of debris in the needle seat holding the needle valve open. Do you have a fuel filter? Or have you done any work on the fuel lines recently? What condition are the rubber fuel lines in? They may be disintegrating on the inside, especially if you've used any gas with alcohol it. If you need to replace the rubber fuel lines use fuel injection hose, it will be gasohol resistant.

If the needle or seat are worn enough to cause the problem, I would put a rebuild kit in the carburetor, probably due to be freshened up.
 
It looks like the O ring that is supposed to seal the primary to secondary transfer tube is not properly seated on the secondary side. It is a fire hazard. The black smoke is another problem with carb as other have said. Chuck
 
Black smoke is an internal leak, such as too high a fuel level caused by a failed or stuck needle/seat or stuck/misadjusted choke. The fuel looks to be what Chuck pointed out, the transfer tube o-ring, or it could be the brass colored plug behind it leaking. Given the nylon washers under the bowl screws, that carb has been touched before. You can get a rebuild kit for about $40 and go through it yourself, or send it out to be rebuilt. Given you show your location as Charlotte, NC, I'm sure you could find a local shop to do a rebuild on a simple Holley 4 barrel.
 
I did not look closely at the picture of his carb. I concur that his transfer tube seals may be leaking. It happened to my Holley in the past. Most hoses made after 1995 are of EPDM composition and will tolerate ethanol. My Holley was made in 1999 and has held up pretty well to alcohol. Always run a fuel filter!
 
I am in agreement with Ron and HemiKiller, with the black smoke you are getting an overly rich Air/Fuel ratio into the combustion chamber(s). As they mentioned, this could be from any one or more of a few issues... An electric choke that is not opening due to a problem with its heating element or the 12 volt switched power that should be powering the electric choke heating element, a leaking needle and seat, a sticking or sinking (leaking) float, or a ruptured Power Valve. For pre-1992 Holleys especially, those Power Valves are notorious for leaking or being ruptured. Beginning in 1992 Hokey began to use a Power valve Protection Circuit for the vacuum channels and Power Valve on the vacuum side of the metering plate/block, which has a spring loaded check ball that keeps high pressure from the intake manifold (due to a backfire or engine burp back) from reaching the Power Valve and damaging its rubber diaphragm. For pre-1992 Holley carbs the Power Valve Protection feature can be added with a kit they sell:

https://www.holley.com/products/tools/carburetor_tools/parts/25-100QFT
If you suspect a ruptured Power Valve you can pull off the front fuel bowl after removing the 4 bolts connecting the fuel bowl and metering block to the main body of the carburetor. Then remove the metering plate. If there is any liquid fuel on the vacuum side of the metering block (where the head of the Power Valve is located) it was leaking raw liquid gasoline into the intake manifold.

Attached are a few files within a Zip file I have put together over the years re: the Holley Power Valve problems. Some of the info in the multiple documents are overlapping, but there is also a lot of non-overlapping info that you may find useful, to include how to test for/diagnose a leaking Power Valve.

In short, if the choke plate is wide open, and you are not seeing gasoline being splattered out of the venturis when you looking into the venturi throats when the engine is idling and belching black smoke, it is likely not a sunk or leaking float or a failing needle and seat. The fuel leak is more likely internal due to a leaking Power Valve. If you are seeing raw fuel being spilled into the venturis when the engine is idling then it is likely the float that is sticking or leaking and sinking, and/or needle and seat that is leaking. More obscure problems can be caused by excessive fuel pressure from the fuel pump that the float, needle, and seat can't shut off.
 

Attachments

  • HolleyPowerValveZipFiles_Archive_20220905.zip
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I was able to get a detailed picture of the model number on the Carb.
I know it's a Holley and the model # is 80457. Thanks for the detailed information and suggestions.
I have been running -non-ethanol and trying to get it out once in a while for a cruise, but it's been crazy hot the last several months.

Any issues with the non-ethanol or could it be me just not running as much? Any additional additives i can add to the gas. Does that stuff actually work?
 
As stated before there is an O-ring on each side of that transfer tube, the rear one is either pinched, broken, or it has hardened and no longer seals. Being that the carb has the nylon washers, it may also have reusable gaskets. I would take out the rear bowl and see if you have the reusable gaskets (they are usually blue), even if you have the more modern Holley gaskets that are brown/tan, they have a coating on them so that they do not stick, if they did not stick you can reuse them. When you remove the rear bowl you can remove the transfer tube and replace the O-rings, you need to put some oil on the O-rings so that they do not get pinched. You can buy just the O-rings:

https://www.summitracing.com/parts/...9doWv5NF_IDQ3E5ErBj_qOSZU1Z08UAYaApgNEALw_wcB
If the carb is running really rich, you probably have debris on a needle and seat, a bad needle and seat, or a float that is way too high and thus it cannot seal. Usually if you have any of these things going on you will have fuel coming out of your boosters at idle. Let the car idle and look down the barrels of the carb, you will probably see drops of fuel coming out of either the front or the rear boosters, if you do, you now know where your problem lies, either in your front or your rear bowl or maybe both (rare for it to be both). If you are lucky, you will have the leaking on the rear boosters, and when you remove the rear bowl to replace the O-ring you can look at the needle and seat and see if there is some debris there. Debris is usually the culprit if the car was running fine before you had any issues, so just remove the debris from the needle and seat, put your new O-rings in place and you are done. The second most common issue is just the float being too high, if its too high just adjust it down. A good rule of thumb on Holley carbs, for initial setup, is to have the floats be parallel with the bowl, you achieve this by turning the bowl upside down and just visually making the bottom of the bowl (since the bowl is upside down it is actually the roof of the bowl) and the float look parallel with each other. You adjust the float level from the outside by screwing in or out the needle and seat adjusting nut and screw. You do the final adjustment of the floats with the car running at idle, where you remove the side fuel bowl plugs and set the float to where the fuel is at the bottom of the threads of the screws and just barely leaks out. You can check to see if your needle and seat are sealing by blowing with your mouth into the opening where the transfer tube goes in (on the rear bowl) and holding the float closed against the needle and seat with very light pressure. If you blow into the bowl with the float closed and the air is escaping, and there is no debris on the needle and seat, you probably need a new needle and seat. They also do sell them separately. On the front bowl you need to blow into the fuel inlet and put a finger on the transfer tube hole to see if you have a good seal.

As stated by mrgmhale, you could also have a sticking or inoperable choke, or a ruptured power valve making the car run rich. On the video you put up the choke is closed, car may have just been cold, but if it was hot, that is why the car is running rich. In my experience a ruptured power valve is quite uncommon, but it does happen, especially if you had some issues with backfiring. I do not see any evidence of black soot on that carb, so I don't believe you had a bout with a backfiring engine.
 
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