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I've rebuild many carbs before, but never had a problem like this. I took carb apart cleaned it, rebuilt it, new needle and seat, seals, float. I adjusted the float, put it all back together and stills have a slow leak. I've read about ethanol eating rubber and aluminum away, so I replaced the bowl and it still leaks. Rebuilt the carb again with another float and still leaks. I've heard ethanol distorting the vapor release in the gas cap causing pressure to build allowing slow leaking. So I loosened the gas cap and still have a slow leak and what I mean by slow leak a drop or two every 3-4 minutes. I've noticed the replacement floats are plastic, is this the problem? Has anyone have this problem?

If the float is good I think you are not getting the float needle seat properly seated. Here is the procedure I use. If you can get a crochet hook and work carefully, you should be able to remove your new Seattle and clean everything and reuse the seat.

Needle and seat replacement

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

Post engine manufacturer as well as all numbers from engine that carburetor attaches to, thanks.

Also, and I'm not saying this is your problem or not, but don't Tecumseh's inlet seats have the two raised circular sections on one side of the seat that must me installed down into the bore?

http://www.barrettsmallengine.com/manual/tecumsehcarburetormanual.pdf

Tecumseh Service Manuals

mechanic mark said:

Post engine manufacturer as well as all numbers from engine that carburetor attaches to, thanks.

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It's a Yardmaster snowthower with a Tecumseh 5.5hp Model: LH195sp Spec: 67517D
The seat is installed properly, and this happened to another carb the exact same way. Ever since ethanol, this started to happen. Also I changed the float back to the brass one and still have the same problem.

There are two basic things which will cause a carb to leak. One is that the float needle is not seating properly. The second is that the gasket between the float bowl and the carb body is not sealing properly. That is where you should concentrate your search.

bluejeans said:

It's a Yardmaster snowthower with a Tecumseh 5.5hp Model: LH195sp Spec: 67517D
The seat is installed properly, and this happened to another carb the exact same way. Ever since ethanol, this started to happen. Also I changed the float back to the brass one and still have the same problem.

Click to expand...

Well I ordered the Tecumseh tool for removal and installation. I'm going to see if it will do a better job then turning the needle around on the flat side to install the seat. If that's the problem.

http://www.barrettsmallengine.com/tecumsehpartslist/LH195SP-67517D.pdf

https://www.google.com/webhp?source...espv=2&ie=UTF-8#q=carburetor tecumseh 640084b

Check this site out: http://outdoorpowerinfo.com/repairs/#id_tecumseh
And pay attention to the direction of the inlet needle clip. Installed wrong, and they will sometimes leak.
As was mentioned, the groove/ring on one side of the rubber seat , must face down, away from the needle!

If you are using the needle to set the seat, you are not going to be able to seat it properly without cutting the oriface. As I said in my earlier post, a drill bit works very well.

Rivets said:

If you are using the needle to set the seat, you are not going to be able to seat it properly without cutting the oriface. As I said in my earlier post, a drill bit works very well.

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great advice i'm going to replace it again trying that method