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I recently took apart my carb because the mower wasn't running well. I had no leaks. I replaced most of the gasket, seals and o rings. The only one I didn’t replace was the small rubber one that the needle sits in. It looked like it was in good enough shape. I did not have a leak beforehand. Well, I put it all together and now I have a leak. However, it’s not sudden. After running the mower and it sits overnight, gas starts to slowly leak out of the slow jet screw. There doesn’t seem to be an o ring in that place. What would be causing this and what should I check next?

That is not an adjustable screw. That is a air bleed jet. It should be lightly seated.

kind of laughing here. I have a edger with the same basic carb and it started draining the tank when the float went bad. About 20 years old at that point. I am really good at carb rebuilding and I rebuilt it three times, and it still leaks slowly. I finally put a new carb on it yesterday, and it runs really well. I have the old one my workbench and maybe I will rebuild it again once I inspect it. One of the things that I did find in ordering parts for the last couple rebuilds, is that some of the replacement parts are worse than the originals. I also had the same carb on a tiller, and although it never leaked, it did need rebuilding a couple times but never had problems with that.

You need special tools to replace the needle seat etc.. I did find this how to which gives some fine tips. https://outdoorpowerinfo.com/repairs/tecumseh_carb_632747.asp

ILENGINE said:

That is not an adjustable screw. That is a air bleed jet. It should be lightly seated.

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I know it’s not adjustable, but it was removed and cleaned out and NOW it leaks out. Go figure.

that is probably a sign something else is going on. That said, my problems with the edger carb began when that screw vibrated loose and fell out. The local shop has a replacement but the internal leak that started then has never stopped.

The level of the fuel in the float bowl is the gasket
If fuel leaks from anywhere above the gasket line then the float valve is not shutting off the fuel , end of story .
If it suddenly happens after you have overhauled the carb then the obvious thing to assume is you have made a mistake in the assembly

bertsmobile1 said:

The level of the fuel in the float bowl is the gasket
If fuel leaks from anywhere above the gasket line then the float valve is not shutting off the fuel , end of story .
If it suddenly happens after you have overhauled the carb then the obvious thing to assume is you have made a mistake in the assembly

Click to expand...

the float level is fine when it runs, and the float is good. But when the fuel is shut off, the fuel in the bowl dissapears when it sits but the exterior of the bottom of the bowl is dry. When the bowl is taken off after sitting a week there is only about 3/8 to 1/2 inch in it. If the fuel is not shut off, the shed will smell of gasoline but nothing will be wet on the outside. Out of the blue it drained a half tank of gasoline the first time it happened before I rebuilt it. That time the jet that holds the carb bowl on was leaking. I replaced it as well as rebuilding the carb. The oil level is fine too, and the oil feels normal. I'll figure it out when I have the time to inspect the old carb for stains. It is not a normal issue. I've rebuild thousands of carbs in my life. I suspect that the bulb is not sealing properly and that is where the fuel vapors are going out. The new carb started really easy where as the old carb I have to push the bulb many more times. I've had trouble getting high quality bulbs. The stuff shipped, even though labeled BS are really pretty poorly formed. The bulb lock rings don't seat well either compared to the original that came with it. They are pretty flimsy.

It has to be the float valve .
It is leaking very slowly so when mowing there is no problem as the fuel is passing through the engine.
So it comes back to the float valve
I invert my carbs and pump them to around 5 to 10 psi then leaves them for an hour or so.
If the pressure has not dropped the carb goes back on the engine
If it has dropped I go looking for the reason
Most times it is the test rig
Occasionally I have to dress the seat on fixed seat carbs then adjust the float if needed .

so explain where the fuel already in the bowl goes cause the fuel already in the bowl disappears even when the fuel is shut off. The first failure as I said earlier was a corrosion pinhole in the 20 year old float that started right after I lost that jet. I test each new float in hot water to be sure it doesn't bubble. Two of three new BS floats leaked but the one in it is good, and the fuel is shut off. Proof is that the bowl is not full when it is removed after sitting a week or two. These carbs have a replaceable seat that a special tool is needed to remove and replace them.