Riding Mower-Gas mixing w/oil-Attn:TOM


Old 04-04-01, 08:30 AM
Thread Starter
Join Date: Mar 2001
Location: Tennessee
Posts: 211
Hi Tom,
My Father-In-Law has a Murray Riding Mower with a 14.5 hp/42" Cut,about 6-7 years old.Briggs/Stratton OHV Engine.He is having problems with gas mixing with the oil.No problems until now.Is there anything other than float/seat worn allowing overflow into oil breather hose or a crack in the combustion chamber/oil chamber wall that would allow the gas to get into the oil. I went over and took out float/seat and cleaned/inspected and they appeared ok and functional.Changed oil and refilled 1/2-3/4 tank of gas and ran it,seemed ok,then he checked oil the next day and it was mixed with gas again,gas tank empty.If it's a crack,is there a solution or is it new mower time? I will have no problem diagnosing/repairing if you could detail the path to take.Thanks in advance.Take Care.

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Old 04-04-01, 05:28 PM
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Hi: CoolBreeze

Excellent question. Difficult to diagnose here in this text only type forum. However, you have discribed it very well.

Regarding the fuel getting into the oil, is there a fuel pump? If so, be sure it is turning off when the ignition is turned off. May also have a vacuum operated fuel shutoff valve.

If the carb is a diaphram pump type, it may have a fuel return line. A restriction in this line could cause fuel pressure to build up, then dump into the engine after shutdown. The return line may be all or part of the problem.

If the fuel is gravity feed, the carb may appear to have a good needle and seat, yet it may not be closing fully. It's also possible the needle and or seat are damage or blocked do to debris in the carbs fuel bowl.

Also inspect the beather vent. Be sure it too is clear and operating correctly.

I have covered several items and fuel delivery systems that may not apply to your specific machine for the benefit of others whom also may read this posting.
Old 04-04-01, 06:30 PM
Thread Starter
Join Date: Mar 2001
Location: Tennessee
Posts: 211
Riding Mower-Gas in Oil

Hi Tom,

Thanks for your quick response. It is Gravity feed and the float/seat/needle being easiest/cheapest,I advised him to get the float kit and I'd change it. If that's not it,what are the chances of it being a crack inside engine wall ? He had no problems until now and heard no unusual sounds when riding a week before.He found it when he went to change oil.Is there anything else inside engine chamber seperating gas/oil compartments that could be worn allowing this.It seems fine running,we watched it a good while with no carb overflow,but seems to do it while off and sitting/not running. Thanks again.

Old 04-04-01, 07:57 PM
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Hello: CoolBreeze

Small engines use a splash oil system. Which means there are tiny spoon like metal extentsions attached to the piston crankshaft bolts. As the engine crank spins, these spoons splash engine crankcase oil around.

Most likely you'll not visually see fuel entering the piston cyclinder area nor fuel coming out of the carb. The fuel enters slowly, almost matches the color of the carbs internal venturi walls. You may smell an excessive amount of gasoline near the machine if it is stored indoors.

Best bet is as you said, which is to replace needle, seat and float. The float pin also needs to be checked.

Corrosion on the pin, float or any pivot points could also be all or part of the problem.

The float isn't likely to be the problem. However, it can be tested. Just float it for several hours. It should still be a float when you re check it. If not, toss it also.
Old 10-01-06, 09:17 AM
Join Date: Oct 2006
Posts: 1
Hello all.

I am having this exact same problem with the exact same mower.

One thing to add. On the bottom of the float bowl is a two wire electrical connector that no one seems to be able to figure out.

I mention this because in addition to the gas tank dumping into the crankcase the battery also goes completety dead.

My guess here is that the electrical connection somehow controls the fuel flow. It shorts out, drains the battery and drains the fuel tank.

Any help?

Old 10-01-06, 10:06 AM
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Hello slipperyskip. Welcome to the Do-It-Yourself Web Site and the Small Engine forum.

The thread is 5+ years old but still a valid question. One that still needs to be addressed and likely to be by the topics professionals.

Regarding the float bowl with wires attached to it. Internal solenoid likely. When not energized with current, it is suppose to close. Likely does but seat worn and/or damaged.

Which allows fuel leakage to occur. Solution is to disassemble carb, rebuild and or replace solenoid. Or may have to replace entire carb. Depending upon parts availability and ones own skill level working with small parts, etc.

Best bet, as a do it yourself project, is to have a service manual. Even one that is generic is better than none. And a very clean work surface area.

Look out for small parts during disassembly. Also note where each part is removed from and how it needs to be reinstalled.

Most likely I haven't covered all of the possibilities. The resident small engine service and repair professionals in the forum may be able to offer additional suggestions, advice & help.

Check back on your question several times over the next few days for additional replies.

Small engine repair parts, generic repair manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Read all already asked questions and the replies offered in them on this same type of problem for additional help & information. Doing so will provide additional possible causes and the solutions to correct them.

If you need further assistance, use the reply button. Using the reply button moves the topic back up to the top of the daily topic list automatically & keeps all communications in this one thread.

During installations of some parts which may not fit exactly perfect, it may be necessary to apply "BRUTE" force in order to compel compliance. {just humor folks.}

Personal Quote:
"If it ain't already broke, don't fix it, tinker with it or $#@&*&%$#@! with it until you do break it!"

Regards & Good Luck. Sharp Advice.
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Opps! 4 got something...
Hi CoolBreeze....
Old 10-01-06, 01:38 PM
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With a "fuel dumping into the crankcase oil" situation, it will be one or two problem areas. First, the inlet needle and seat are no longer functioning properly and thereby not stopping the fuel flow as necessary. And secondly, the float could have a hole in it whereas it no longer floats and, again, allows fuel to continually flow. The wires running to the electrical component attached to the float bowl is a fuel solenoid. Its purpose is to reduce the liklihood of afterfire (bang) after the engine is shut down. This may be the source of your excessive current draw but I doubt it. I'd be more inclined to say you have a battery in need of replacing. If you think not, then you'll need to test the output of the regulator and/or the stator. As for the carburetor is concerned, I recommend a soaking in a bath-type cleaner (I like Napa's #6402) and reconditioning with a genuine OE kit and be sure to shake the float for any signs of fluid in such and replace this, if necessary. Because the float is not included in any kit you'll buy, you'll need to purchase it seperately.
Old 10-01-06, 06:46 PM
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And may I suggest a manual fuel flow shutoff valve.
Old 10-02-06, 06:51 AM
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A manual shut off valve may keep the tank from going dry but won't provide any help for the symptoms if the other two designed fuel valves are not working properly.
If the float has a leak you should be able to shake it and hear sloshing. If no sloshing and it is still suspect, submerge it for a time in gas. Gas will leak into holes that water and other fluids will not.
The float, needle valve and seat are the final stopping point for fuel flow so as long as there is fuel mixing in the crankcase, its almost certain that there is a problem with that assy. Even if the soleonoid fails, the needle valve should keep the fuel level in the bowl low enough as to not get high enough to leak out the top of the carb into the engine.

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