Crankcase keeps filling with gas


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Old 10-19-18, 09:42 AM
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Crankcase keeps filling with gas

I have a tecumseh 358cc ohv engine in an ariens rider. Crankcase keeps filling with gas. I rebuilt the carb 3 times thinking need and seat is not shutting off gas and then sucking up through exhaust and filling up crankcase then comes through breather and chokes out engine. After each rebuild I drained and put fresh oil in and just does the same thing so I bought a new carb and put that on and changed oil. Well this time engine ran for 20 minutes before spitting gas through breather so I just shut it off. After each rebuild it would run around 10 minutes before chocking out. What else am I missing? I did replace fuel filter as well thinking dirt was keeping needle from seating? Any advice would be appreciated. Thanks
 
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Old 10-19-18, 10:15 AM
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If that has a fuel pump driven out of the crankcase either mechanically or vacuum pulse, that's likely where the fuel is getting into the crankcase.
 
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Old 10-19-18, 10:18 AM
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And each time you've re-built the Carburetor, you've replaced the Float Needle and Seat ?

This movement of fuel into the Crankcase is pretty common with an ill-seating Float Needle . . . . I once had one sit long enough to have the exchange of Oil up into the gas tank !

It's usually the Float Needle.
 
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Old 10-19-18, 02:01 PM
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That's what I thought but like I said I rebuilt the carb 3 times and now just put a new carburetor on and it still does the same thing. It's not an electronic fuel pump either just regular fuel pump. This has happened to many other engines and all I do is rebuild the carbs as the needle is not seating and allowing gas to keep flowing into carburetor and then up exhaust Port into crankcase and this always solve the problem before but not on this engine for some reason it must be something else?
 
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Old 10-19-18, 02:06 PM
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The fuel pump is vacuum pulse driven? If so the diaphragm is likely leaking fuel into the crankcase.
 
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Old 10-19-18, 02:06 PM
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It has an external fuel pump mounted on outside of engine. Gas tank is under tractor and lower than engine but no oil goes into tank and yes it's a new needle and seat Everytime with a good carb cleaning and soak.
 
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Old 10-19-18, 02:09 PM
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Even if diaphragm was leaking fuel it's mounted on outside of engine on crankcase cover and would leak on the ground not in crankcase?
 
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Old 10-19-18, 02:11 PM
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Bad fuel pump diaphragm leaking into crankcase. It leaks through the pulse line. If the pump is mounted on a crankcase port, it leaks directly into the port/crankcase.

Snowmobiles do it all the time.
 
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Old 10-19-18, 02:31 PM
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Sorry I said that wrong fuel pump is mounted on outside of shroud with 2 little screws. The fuel line then runs to carb. If you take the 2 screws out fuel pump is of engine. They r just mounting screws so if diaphragm is leaking i don't see how it gets in the crankcase. It should just leak on the ground?
 
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Old 10-19-18, 02:44 PM
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Ok you are saying that diaphragm is leaking and gas is going in the vacuum that runs pump than filling crankcase?
 
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Old 10-19-18, 03:50 PM
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Yup. There are different types of fuel pumps. Electric are completely separate from the crankcase, mechanical have a diaphragm often driven by a cam lobe or similar inside the engine. The last type is the vacuum pulse type which has a diaphragm driven by the pules coming out of the crankcase.

You have that type on two stroke and four stroke, but both work about the same. The pulses coming off the piston moving up and down drive the pump diaphragm. The pulse is carried to the pump either by a line or a port on the side of the crankcase. On small engine two strokes, that vacuum port and fuel pump is integrated in the carburetor. A lot of four strokes use the vacuum line going to the pump.

When there is a leak in the fuel diaphragm, it lets fuel into the pulsing side and fuel is drawn into the crankcase. The pulse is very fast so there is enough to drive the fuel to run the engine and still allow the gas into the crankcase.
 
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Old 10-19-18, 04:13 PM
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The fuel pump will leak gas into the crankcase through the pulse line going to the fuel pump. It's a common reason for gas getting into the oil.
 
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Old 10-19-18, 05:58 PM
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Yes thank you. I never noticed the vacuum line running to the pump it's hiding behind and under pump. Will get new one and give that a try which has to be the culprit
 
 

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