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Leaking Carburetor

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Leaking Carburetor

Postby dennis » Wed Sep 19, 2018 10:05 am

A friend has a Twin II L-Head Briggs and Stratton 18HP engine, model 422435, type 1199-01, code 87112412. The carburetor fuel pump cover has two tiny vent holes that are seeping gasoline. Could this be caused by a hole in the pump diaphragm? Could it be caused by a sticking float or dirt under the inlet needle? To remove the carburetor, I read that you have to remove the intake manifold first (with the carb on it). If the problem is a leaking pump diaphragm, can the diaphragm be replaced by just removing the 3-screw fuel pump cover without removing the intake manifold and carb?
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Re: Leaking Carburetor

Postby RoyM » Wed Sep 19, 2018 10:16 am

You are correct, the diaphragm is leaking. The pump can be repaired on the unit as long as you are careful not to drop parts.
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Re: Leaking Carburetor

Postby KE4AVB » Wed Sep 19, 2018 10:32 am

As Roy said just be very careful as there are two tiny springs involved.
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Re: Leaking Carburetor

Postby dennis » Wed Sep 19, 2018 11:05 am

Thanks Roy and KE4AVB. When you don't do this stuff all the time, it helps to get good pointers. Thanks again.
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Re: Leaking Carburetor

Postby Skywatcher » Wed Sep 19, 2018 1:43 pm

Hi Dennis

If fuel is leaking from the vent holes, the surge diaphragm is the most likely culprit. The fuel pump is upstream of the needle and seat, so you probably won't have to take the carburetor off. Pay attention to what Roy and KE4 say, these parts are tiny and get lost very easily. I would recommend buying a pump repair kit and studying it before you take the pump to pieces so you know what you're going to find in there once you open it up. My guess is you'll need B&S part # 393397 or Stens # 520-106. Partstree.com has a pretty good picture of the kit if you enter the B&S number into the (search by part number) field on the top left of the page, you'll see the tiny springs we're talking about. Best of luck,

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Re: Leaking Carburetor

Postby dennis » Wed Sep 19, 2018 7:01 pm

Thanks, Skywatcher. I will do that. So you are saying that a leaking needle valve would not put fuel through the vent holes?
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Re: Leaking Carburetor

Postby StarTech » Wed Sep 19, 2018 7:21 pm

dennis wrote:Thanks, Skywatcher. I will do that. So you are saying that a leaking needle valve would not put fuel through the vent holes?

Dennis think of it as like the hockey puck fuel Briggs now uses. The only difference is it is made as part of the carburetor. It is a fuel so it must be before the float valve otherwise fuel would be going everywhere as there would no flow control.
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Re: Leaking Carburetor

Postby dennis » Thu Sep 20, 2018 11:24 am

Got it, Starfire. Good description. Took me awhile to figure out what you were saying. I think you meant hockey puck fuel pump. Thanks.
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Re: Leaking Carburetor

Postby Arkie » Fri Sep 21, 2018 4:28 am

dennis wrote:A friend has a Twin II L-Head Briggs and Stratton 18HP engine, model 422435, type 1199-01, code 87112412. The carburetor fuel pump cover has two tiny vent holes that are seeping gasoline. Could this be caused by a hole in the pump diaphragm? Could it be caused by a sticking float or dirt under the inlet needle? To remove the carburetor, I read that you have to remove the intake manifold first (with the carb on it). If the problem is a leaking pump diaphragm, can the diaphragm be replaced by just removing the 3-screw fuel pump cover without removing the intake manifold and carb?


Just some tips from experience:
No need in removing the intake on that Briggs l-head opposed twin engine to remove the carb. You may have to remove the mower's hood for easier access. You will need a 1/4 inch drive socket set, 3/8 socket and extensions to remove the carb bolts. (they are accessible from the bottom of the carb and if they are torx use a 3/8 socket or a torx adapter. Torx is more user friendly.

The 3 screw fuel pump is bad and since you have never been into one you most likely need to remove the carb and go to a clean workbench. You will need a 393397 fuel pump kit. You can look at exploded views of the 3 screw pump so as too get an idea of the layout.
You can use little dab of vaseline to hold the itty bitty springs in place and in the kit sometimes both springs are wound together to look like one spring AND if you put it back on the mower and it's still leaking you did not get the front cover and diaphragm correct. (sometimes the front diaphragm is not user friendly to get in place for a seal at it's very lower edge)

You can try it while on the mower but just be aware that you will most likely have to remove the carb.

Be careful when re-installing the carb, the plastic adapter under the carb has a little locator pin that goes down to help hold and align the adapter. If you break any of the mounting gaskets. just get a piece of cereal box cardboard and make the gasket using the other one as a pattern.

Have patience when re-installing. Once you have done one the next time will be more user friendly.
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Re: Leaking Carburetor

Postby 38racing » Fri Sep 21, 2018 8:26 am

Dont know if still true but carb kit for 3 bolt was mucher cheaper than 4 bolt.
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