Carburetor overflow

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Carburetor overflow

Postby farmalldean » Mon Apr 15, 2013 5:49 pm

1957 Cub restored in '94 including rebuilding carb. Rebuilt carb 2-3 x since due to carb overflow. Cub runs good but is rich starting and must shut gas off if engine off more than a few minutes.
Searched the topic. I think I should check the float in hot water. Any suggestions of other things to check? It runs excellent just can't leave it without shutting off gas.
Where can I buy a new gasket without getting whole rebuild kit?
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Re: Carburetor overflow

Postby Lurker Carl » Mon Apr 15, 2013 5:56 pm

When the carburetor leaks AND the cause is not a sinking float or defective needle, you have internal leaks within the carburetor. Corroded gasket seats for the needle cage and fuel nozzle are typical culprits.
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Re: Carburetor overflow

Postby Rudi » Mon Apr 15, 2013 6:09 pm

Echo Carl's comments. If you do not want a complete kit, then I would recommend that you buy the individual parts you require from Tom and Lynn at TM Tractor Parts - one of our site sponsors and great folks to boot. Their service is top notch and they stand behind every product they stock.
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Re: Carburetor overflow

Postby farmalldean » Mon Apr 15, 2013 7:18 pm

Can you expand on the corroded gasket seats for the fuel nozzle and needle cage? The carb body looked like new as I recall when I cleaned it up. I will check carefully when I open it up.
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Re: Carburetor overflow

Postby cub47 » Mon Apr 15, 2013 7:30 pm

farmalldean wrote:Can you expand on the corroded gasket seats for the fuel nozzle and needle cage? The carb body looked like new as I recall when I cleaned it up. I will check carefully when I open it up.


Carl has an excellent pictorial how-to on Rudi's site located here regarding this:

http://www.cleancomputes.com/Cub/Mainte ... /frame.htm
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Re: Carburetor overflow

Postby challenger » Mon Apr 15, 2013 8:25 pm

Here are some thoughts. With reference to your wanting a new carburetor gasket, keep in mind that no carburetor gasket can control a flooding carburetor. It is the job of the float to keep the bowl approximately half full of gasoline so a carburetor gasket is not your problem. If you have gasoline running out of the carb. there is a gas flow control issue. It could be a leaking float that no longer floats, gasoline leaking into the bowl though a flaw in the pot metal of the carburetor gasoline channel leading to the needle valve, or a malfunctioning needle valve/seat.

If you suspect a leaking float, the first thing to do is shake it and listen for gas inside. You can otherwise test it by putting it in a plastic bag and chilling it with ice and then quickly taking it out of the bag and submerging it in warm water and watching for air bubbles. The expanding air bubbles will tell you if and where there is a leak in the float.

You can test for a flaw in the gas channel by removing the needle valve seat from the carb and plugging the port with your finger while holding the carb up so you can fill the gas channel with water and then carefully examine if there is any leakage along and around the channel leading to the needle valve port. Another way to test the channel would be to use compressed air. Hold your finger over the needle valve port, submerge the carb top in water and introduce compressed air into the gas inlet to the carburetor and look for air bubbles escaping.

The malfunctioning needle valve is a common problem most often caused by sediment getting between the needle and the seat. The needle and seat could also be worn or damaged somehow preventing a complete gas shutoff. Another possibility, but less likely is that the float is so out of alignment inside the carburetor bowl that it is getting hung up somehow and not moving freely as required.
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Re: Carburetor overflow

Postby Lurker Carl » Tue Apr 16, 2013 6:43 am

A gasket seat is the flat part surrounding an oriface where the gasket sits against the casting. It should be smooth but after 50 years tends to have pocks and crevices that allows gas to seep past the gasket. Some seats can be cleaned up but most need a tiny coating of silicone on the gasket facing the seat to fill the imperfections. I can not over emphasize using as little silicone as possible, globs of silicone moving around your carburetor will create some new and different problems. When dealing with carburetors, cleanliness is paramount.

The needle cage is the brass thing holding the float needle. The fuel nozzle is the tube sticking up in the venturi.
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Re: Carburetor overflow

Postby cub47 » Tue Apr 16, 2013 7:10 am

cubguy47 wrote:
farmalldean wrote:Can you expand on the corroded gasket seats for the fuel nozzle and needle cage? The carb body looked like new as I recall when I cleaned it up. I will check carefully when I open it up.


Carl has an excellent pictorial how-to on Rudi's site located here regarding this:

http://www.cleancomputes.com/Cub/Mainte ... /frame.htm


And I believe this slideshow only works on the Internet Explorer browser.
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Re: Carburetor overflow

Postby farmalldean » Tue Apr 16, 2013 11:47 am

Thank You for all the help. I remember some of you when I had a clutch problem which you solved. Rudy's pictures and detailed instructions are excellent. I found the Kohler carb kit 25-757-02-S on Amazon. I will copy off all your suggestions and take one at a time and make sure the problem is solved!
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Re: Carburetor overflow

Postby Eugene » Tue Apr 16, 2013 12:04 pm

farmalldean wrote:I found the Kohler carb kit 25-757-02-S on Amazon.
Kohler kit as in Cub Cadets? Thinking we should have asked what type of engine before we answered the questions.

You can purchase individual, needed Kohler carburetor parts from your auto parts store.
Last edited by Eugene on Tue Apr 16, 2013 12:07 pm, edited 1 time in total.
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Re: Carburetor overflow

Postby farmalldean » Tue Apr 16, 2013 12:07 pm

I have been using denatured alcohol to clean the carbs. Is that a good method or is there a better chemical?
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Re: Carburetor overflow

Postby Eugene » Tue Apr 16, 2013 12:11 pm

Pick up a spray can of carburetor cleaner at your auto parts store. You can clean the galleries with it as well as external surfaces.

I use the spray cans for fairly clean carburetors. For carburetors requiring a soak I use the gallon container of solvent.
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Re: Carburetor overflow

Postby farmalldean » Tue Apr 16, 2013 12:12 pm

Eugene wrote:
farmalldean wrote:I found the Kohler carb kit 25-757-02-S on Amazon.
Kohler kit as in Cub Cadets? Thinking we should have asked what type of engine before we answered the questions.

You can purchase individual, needed Kohler carburetor parts from your auto parts store.

As I understand it the Kohler small engine repair kit has a float valve cage and needle that fit the Cub and it is superior to the Cub float valve assembly.
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Re: Carburetor overflow

Postby Jim Becker » Tue Apr 16, 2013 12:31 pm

farmalldean wrote:
Eugene wrote:
farmalldean wrote:I found the Kohler carb kit 25-757-02-S on Amazon.
Kohler kit as in Cub Cadets? Thinking we should have asked what type of engine before we answered the questions.

You can purchase individual, needed Kohler carburetor parts from your auto parts store.

As I understand it the Kohler small engine repair kit has a float valve cage and needle that fit the Cub and it is superior to the Cub float valve assembly.

I have used the Kohler needle and seat and been happy with how it works. It is a viton tipped needle and was the prefered choice when everyone thought viton was the answer. (I still like the viton tipped needles.) One thing to be careful of, the Kohler needles I have run into are much different than the Cub originals. Be sure to use both Kohler parts together. The assembled length is the same as the original. Keeping needle and seat pairs together is a good idea, even when the lengths are the same.
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Re: Carburetor overflow

Postby Eugene » Tue Apr 16, 2013 12:36 pm

Needle valve and seat. Federated and NAPA part number 7-02306 for K series up to 12 hp. 7-02326 for 14 and 16 hp engines.

Take in your old needle valve and seat to be matched up.

If you have the metal needle valve tip - you can lap the needle valve to the seat. My preferred method.
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