Fuel dripping from Carburetor

[eurban]

New member here and this is my first post!

Issue: AFTER SHUTOFF, fuel partially fills flame arrestor housing and drips from choke shaft. This occurs even with the fuel shutoff and since the engine is off, the electric fuel pump is not operating

Background:
Gasoline atomic A4 with late mode Zenith Carburetor
Installed in 27' 1976 Tartan
Gas tank is stainless steel situated above the engine, inline shut off directly below the tank
Electric Fuel pump
Racor water separator / filter


We have owned the boat for about ten years but have recently had a child and the boat has seen little use for the past 4 years. Most recently, our engine has not been running well and the cabin has been smelling of gasoline. Fuel pumped from the carburetor supply line in to a container separates into layers suggest water contamination

In the interest of fixing the issues I have:

Replaced the fuel cap seal in the cockpit. During heavy rains our cockpit will have some water in it and I suspect that some has been getting past the cap seal.

Old fuel has been removed from the tank and replaced with fresh. The filter element for the Racor has been just replaced and a new polishing filter has been installed between the fuel pump (sediment bowl emptied and cleaned) and carburetor. I have also jumpered the fuel pump and ran the fresh fuel through the system, filling up a pint (or so) container. Fuel looks good now.

I have cleaned and rebuilt the carburetor using the Moyer Marine kit for the late model carbs. A new float needle and seat has been installed and I have "burnished" the seat on two separate occasions in the hopes of improving any sealing issues. The float sits parallel to the carb body when held upside but I have not measured the pontoon heights. All new gaskets, seals and jets that come with the rebuild kit have been installed.

Upon carb reinstallation (I have had it on and off twice) the engine starts easily needing little choke and runs well at throttle and idle. Upon shutoff, all seems well for 10 minutes or so but eventually gas begins to flow into the air intake bore / flame arrestor housing and drip out of the choke plate shaft penetrations. Shutting off the fuel underneath the tank doesn't stop the issue.

After the recent rebuild I removed the carb and rechecked my work. I also burnished the needle seat a second time and checked again the float was parallel to the carb body. I also bench tested the carb assembly with a lawn mower gas tank held above it supplying gas to the carb. It seemed OK after sitting for five minutes. Upon reinstall the issue is the same!

QUESTIONS:

Do I need to do more "burnishing" of the the seat? I simply twisted the supplied hardwood dowel back and forth a few times on two separate occasions. Everything looks OK.

Is my fuel supply still bad? As far as I can tell, there is clean fuel now being supplied to the carb. Stainless steel tank with fresh gas going through a new Racor fuel element and then through a new polishing filter appears to be giving me nice looking gasoline when I pump it into a container. Is there anything more I should do here?

Do I need to change the float height? If I was to increase the distance between the carb body and the pontoon (by bending the float), it should lower the level of fuel in the carb. Perhaps my fuel level is set too high in spite of float being parallel to the carb body?? Or perhaps my float is leaking? I can feel absolutely no liquid in side the float when I shake it. Could it still have a leak? Should I just buy a new float? Basically the overflowing issues have persisted in spite of the carburetor rebuild. During the rebuild I didn't change the float setting (it seemed correct) or replace the float so perhaps this points to the float being the issue??

Should I give up on this carb and buy a rebuilt one from Moyer?

Should I hang myself? Getting a little frustrated!

Thanks for any and all thoughts!

Eric

[romantic comedy]

If the shut off valve does not stop the gas flow and the needle is not seating, the gas would overflow....and give you this issue.

This would also mean that the gas is overflowing while the engine is running, and the engine would be running rich.

Problem is that you said that you bench checked the carb.

If the float level is too low, the bowl will fill to high and overflow. You could try adjusting the float level. But where is fuel coming from with the valve off? Check that valve.

did you try throwing wrenches?

[ndutton]

For safety the fuel shut off valve is best positioned immediately ahead of the carburetor. Regarding your carburetor overflowing, during your rebuilds did you check for leaky floats (fluid inside the floats)?

[Al Schober]

Eric,
First, welcome to the forum. We're here to help (well, we try..).
I feel your frustration. I've had all those issues - more than once.
First concern would be the valve - it's not closing. A bilge full of gasoline is a scary thing (run away...). I've installed a 1/4" ball valve on the inlet to my Racor. Location isn't important, but it's gotta work and should be easily accessible. I've gotten into the habit of closing the valve whenever I'm leaving the boat.
The float in the bowl is easy to check for leaks - just put the bowl into a cup of hot water. If it bubbles, it leaks and needs replacement.
The float valve should close off the fuel flow into the carb. You've cleaned the seat, so that should be OK. Does the needle have it's rubber tip? How about the gasket between the seat and the carb body? Also look for any wacky thing that would cause the float to hang up and not seat the needle.
Last thing I can think of is the pressure from the pump being too high. I'm currently using an electric pump and have a small pressure gauge at the carb inlet. My carb is happy with the pump delivering just under 4 psi. Perhaps your pressure is too high and is overpowering the float valve? The mechanical pumps have a diaphragm which could stiffen due to exposure to alcohol fuels and give excess pressure.

[eurban]

Thanks for the thoughts!

Just to reiterate, I have rebuilt the carb using Moyers kit so it has a new needle seat, new needle seat seal and new needle installed. The float does not appear to have any fluid in it when you hold it and shake. Engine is equipped with an electric fuel pump that looks just like the setup in the Moyer kit.

My current fuel shutoff is directly after the tank. I do think that it actually works but that there is a decent amount of fuel contained in the fuel lines, top part of the Racor assembly etc etc that are all higher than the carb and could conceivably trickle down and drip out of the carb. When I jumper the fuel pump to test for fuel quality, fuel will only pump out when the valve is open. Also, when I shut off the fuel below the tank, disconnect the fuel line from the carb and hold the line up high (higher than the carb but still below the tank) no fuel comes out of the hose. Seems like the shutoff works and that it is just the residual fuel in the lines than trickles out.


I don't have a good explanation as to why I seemed to get proper sealing when I bench tested the assembly but once installed the issue continues. Perhaps I just didn't wait long enough or look carefully enough? If the boats fuel supply was the issue that might explain it as well but as far as I can tell it is OK.

I am wondering about how the fuel scavenge system actually works. Is it only effective when the engine is running / pulling a vacuum through the intake system or should it keep the intake bore clear of fuel even with the engine off? If it only sucks fuel with the engine running then this could well explain why the overflowing issue is only apparent after the engine is shut off.

If the issue was too much fuel pressure from the pump, wouldn't that cease to be an issue as soon as the engine is turned off? I know for certain that my electric fuel pump is functioning correctly in the sense that it only operates when the engine is turning.

Overall, it really seems that I either have an issue with the float / float height setting or an issue with sealing ability of the needle.

Float: Can it have a leak even though I can't feel any liquid in side it? I can do the boiling water test of it if that is worth the effort. I will have to bring the carb back home to do this. I can also adjust the float height setting so that the pontoons sit a bit higher when the carb is held up side down and the needle is seated in its bore.

Needle seating: In the FAQ section Moyer talks about needing to burnish the seat even on brand new parts. The carb rebuild kit comes with the pointed hardwood dowl to do the burnishing. How much work should this take?

If the fuel level in the bowl is indeed too high all the time then as mentioned by Romantic the setup should be running rich. From a "cold start" (it is in the 90s here in the mid atlantic) The engine starts very easily and did not want choke for much time all so perhaps this is a sign of being too rich. How much choke should be required and for how long?

Where to go from here? I will install an inline shutoff right before the carb. I suppose at each shut down, I can simply turn it off while the engine is idling and let the engine starve for fuel. This will at least keep me from having dripping fuel and fumes. Assuming the fuel level is always too high, then this doesn't really address the root problem nor does it keep the engine from wasting fuel / running rich during operation. . .

Should I keep burnishing the seat till I'm blue in the face?
Should I adjust the float level for a lower fuel level in the bowl? I thought I remembered reading about a recommended "lower fuel level than than spec" float setting. How is this measured exactly?
Should I pull the float and set in boiling water?
All of the above? I'm beginning to think that this is the correct answer . . .

Thanks in advance for any more thoughts!

Eric

[JOHN COOKSON]

Should I hang myself? Getting a little frustrated!Eric

Rather than hang yourself sacrifice a live chicken* and sprinkle some of the blood on the carb. Then make an offering of beer and fruit to the gods.
*I guess a sea gull might work in a pinch.
After you have done this get a shutoff valve that works. It's obvious you are siphoning fuel out of the tank or something higher than the carb that is getting past the float needle valve. If the tank is a lot higher than the carb it is possible you are getting so much pressure from the siphon that you are overwhelming the needle valve. Try balancing the float on the little bar that connects the pontoons. You will find out real quick if one of the pontoons is leaking.
I set my float drop at 1 5\32 " If you can possibly find a drill bit this size it it will make it easy to measure. Remember to make this measurement with no gasket installed. Also the floats should be parallel to the carburetor body.

TRUE GRIT

[capnward]

mind the gap

Eric,
No need to boil water, just put the floats under water, and if there is a leak it will bubble. I don't see how the temperature of the water matters, but maybe warmer water compresses the floats and forces out air. It could be your floats are not the right distance away from the carb body, although parallel to it, and that the gap needs to be increased, to close the needle when there is less fuel in the bowl. (I think I have that right...) Others can tell you what that gap distance should be. I have seen a diagram for it somewhere on this forum. Mr. Cookson says 15/32", which seems about right. Be careful you don't move the part of the bracket that touches the needle, further from the needle.
Your new needle and seat are probably fine, as long as the rubber tip on the needle looks good. Burnishing the seat with the dowel should just take a moment. It's meant to dislodge dirt, not remove burrs in the brass, which shouldn't exist in a new float valve.
The fuel scavenger pick up only works when engine is running, creating a vacuum.
I doubt your electric pump is making too much pressure. I have a mechanical one, which I believe creates more suction, but not too much pressure. Having a fuel pressure gauge just before the carb is a good thing. So is a shut off valve there.
My engine just requires full choke at a cold start, but choke can be fully opened as soon as it's running. Others keep the mixture so lean that they need to leave the choke closed for a while. My plugs are not fouling so I don't think my mixture is too rich.
Some gas in the flame arrestor housing is ok, but gas should definitely not be dripping from the choke shaft. I have had that happen when it's unsuccessful starting after several tries. Have an oil pad under the carb to absorb any drips and keep gas out of the bilge.
Since your needle and seat are new, and you have been burnishing the tar out of it, and you can't hear liquid sloshing in the floats, my guess is the float bracket got slightly bent during reassembly. It's easily done. I don't know what else the cause of your leak could be, unless it's a gasket problem between the two halves of the carb..
Keep at it, you're almost there. No bird sacrifices are required. A bit of your own blood on the carb is most favored by the gods. Don't ask me how I know. Swearing was involved. Also, an offering of beer is beneficial, but not in the flame arrestor. Offer it to yourself, you deserve it.

[tac]

It sounds like you may have what is an occasional problem with the Zenith carburetor. I ran into similar fuel leakage about 12 years ago (also after rebuilding the carb). I talked to Don who immediately pinpointed the problem and solution. See:

http://www.moyermarine.com/pressure_regulation.htm

Especially the section titled:
REMEDIATING CARBURETOR INTERNAL PRESSURE REGULATION

There have been several threads over the last few years about this, including how flat the carb halves need to be, how much to file off, etc. Some of those threads go into some detail over getting a good fit. Try searching the Fuel System Forum. I think Dave Neptune had the best description/advice.

[roadnsky]

Should I keep burnishing the seat till I'm blue in the face?
Should I adjust the float level for a lower fuel level in the bowl? I thought I remembered reading about a recommended "lower fuel level than than spec" float setting. How is this measured exactly?
Should I pull the float and set in boiling water?
All of the above? I'm beginning to think that this is the correct answer . . .

Eric-
As John said, the factory setting is 1 5/32" to the bottom of the float.
The part you remembered reading about setting a lower level was on Dave's recommendation.
I'll quote him here for your benefit... (hope you don't mind Dave )

"I suggest that if anything, you set the float a bit HIGH @ 1 3/16~1 5/32.
These adjustments are important to control the emulsion wells that mix air into the fuel to break it up! The factory adjustment specs are 1 5/32 +/_ 1/32" which is why you need it to be as parallel as possible. I run mine at 1 7/32 and like the way it performs."

Because you don't actually know what your float level is set at, would be enough for me to open the carb up yet again (I know, frustrating) to check and set it to a known level.

I agree with John that the height of your fuel tank likely creates too much pressure and overwhelms the needle valve.
That would answer your question as to why the bench test didn't give you the same results.
Putting a shutoff valve just before the carb would fix this and is a good safety measure to boot.
Another simple test would be to use a temporary alternate fuel supply (5 gal fuel can) and have it at a lower level than your current tank. See if you still get the fuel overflow.
If you want to go thru the exercise just as an experiment.

QUESTION: Is your carb a FOUR bolt or a FIVE?

Keep at it, you're almost there.

[eurban]

Great thoughts everyone!

My current plan is to install a new inline shutoff (I already have a suitable one from another application) just before the carb. I will actually do this tomorrow so that I can be sure to have no leaking fuel or fumes (I will run the engine till it dies after turning the new shutoff off)

I am also going to order up a new float from Moyer. Most likely my current one is leak free but I want to minimize the need for multiple carb removals and for $20 or so a new part might save me from an additional "non recreational" trip to boat for more carb work. Once I have this part i will pull the carb, measure / set the new float's height and triple check everthing else about the carb. My carb is a 4 bolt one and when I had it on the bench last week, I did wet sand the surfaces on a piece of plate glass to flatten them out and clean them up. I also applied a small amount of sealant around the area where the latest versions have the 5th bolt.

As to the issues of pressure build up from the tank's high location . . .I don't know if the tartans came with a stainless tank from the factory but most certainly the tank arrangement has been in use for a very long time and the setup has functioned OK for much of its life, including four or five years of our ownership. Unless something has gone bad in the existing system (some sort of check valve or vent?) then I can't really blame the tank arrangement for my issues. It may be that my setup does put the needle closer to the "edge" when it comes to flooding. Bottom line is that the needle / float setup should be up to the task of keeping the fuel level correct and that something is currently amiss.

Once I get the new float in and set to spec, if I still have issues with flooding, then I will have to start down the path of mysterious over pressurization. Installing a fuel pressure gauge would probably be the next step.

We will see . . . .

[ndutton]

Eric, when you're disassembling the carb have a keen eye out for debris in the bowl. Even the smallest speck lodged on the float valve will allow fuel to pass via gravity pressure. If debris is present you'll need to find where it came from.

I'm glad you're seeing the manual valve as a safety measure rather than a solution to this problem.

[eurban]

Thanks for the reminder. With the new polishing filter right before the carb I would hope not to have any perceptible contaminants. Fuel lines are less than 10 years old but I did just purchase enough to do a full replacement if needed. . .

In my Tartan's setup, draining the bowl is a real PIA with very poor access to the drain plug and no real room to hold a container underneath. Has anyone replaced their bowl drain plug with some sort of fitting to make things easier to drain? In my setup I could see installing a brass 90degree fitting with a hose barb on it to connect to a short length of hose and then to an inline shutoff and then to a longer hose to allow easy draining into a container.

This would be an easy way to inspect the fuel quality actually seen at the carb itself. End of the season carb draining would be a piece of cake and if the needle does get held open by some junk a few moments of flushing with the bowl drain open should do the trick.

Of course its another failure point but given my current difficulties it seems like a useful addition!

Off to the boat to install the shutoff valve before the carb; so what if its 100 degrees!

[romantic comedy]

Eric, you could also use that bowl drain hose to check the fuel level in the bow. Use clear tubing and hold it up. The level in the bowl with be the level in the tube. (as long as the end if open)

[eurban]

Good idea! I have actually used this trick a number of times on my 78 CB750 motorcycle. Best way to get all 4 carbs to have the exact same fuel level in the bowls. Its what my Dad would have called a "reality method"

Today I got the inline shutoff installed. For kicks I ran the engine till "death" first with just the new shut off and then just with the under tank shut off. . .

The engine quit pretty quickly with the fuel cut off right before the carb. It also started back up with very little cranking once the valve was opened back up. With the under tank shutoff it took a couple of minutes for the engine to die, and then a good bit of cranking to start the engine later. I did wait over an hour before restarting the engine and had no issues with flooding so I do feel confident that the under tank shutoff functions properly, there is just simply a large volume of fuel in the lines, Racor upper assembly, etc. All this residual fuel that is after the shutoff would overflow out of the carb (in its current state) if I let it. The entire contents of my gas tank on the other side of the shutoff, however, would not. Regardless, the new shutoff is a good addition for both safety and convenience.

I'll update more once I receive the new float and get it installed / adjusted. . .

[romantic comedy]

That fuel in the lines should not run out, as air cant get in.

Another thing, and you might get this because of the 750.. Sometimes when you hook up the carb, a hose barb can scrape a tiny piece off the hose, and it gets stuck in the needle valve. Happens a lot on bikes.