500 series push mower, gas in the oil

[Nessuno]

Old mower (sister n'law's) was sitting outside for a couple of years. Have a young niece who needed a mower so I thought I would try and get this one running for her. It is extremely light and easy to push.

Brand: MTD walk behind push mower
Mower Model: 11A-084E020
Engine: Briggs and Stratton 500 series
Carburetor Model: 795477 (This is the setup that has the plastic carb directly on top of the metal gas tank. No float/bowl/needle.)

Short version:
What can cause gas to get into the oil? Bad ring allowing gas to get mixed with the oil?

Long version:
Didn't want to start. Here's what I've done, not necessarily in this order:

1. Changed oil. The old oil did not look healthy. Looked as if there was water or gas in it. Thought I smelled a little gas in it and don't see how water could have gotten in there.
2. Compression tested with a schrader compression gauge: 90psi and held for a minute without dropping.
3. Pulled the magneto, cleaned it up with a wire brush including engine mounts, tested with ohm meter. Good. Remounted with proper spacing using a business card.
4. Checked spark plug with ohm meter and checked for spark. Good. Tested with plug out of engine, ignition wire attached to plug, in a dark garage. Could both hear and see spark.
5. Tested kill switch and kill switch wire to magento to make sure it wasn't grounding. Good.
6. I cleaned out the carb real well. Did NOT put in new diaphragm or gaskets. They seemed workable and I didn't have any immediately available.
7. Cleaned the gas tank while I had it off the engine.

Finally did get it to start but the RPMs were very low. It was hard to get started at all. Had a backfire or two also. So I thought, "maybe the muffler is all gunked up and it can't breath". So I put a new muffler on it (needed it anyway). Still low RPMs. Took a screw driver and held the throttle open. Started up and ran steady with very high RPMs. Took off air cleaner, looked at governor and saw that things were all messed up. The idle spring wasn't attached to the proper place. The governor blade/throttle shaft connecting rod was backwards. After getting that all straightened out and making a few adjustments, the mower runs great.

Mowed my front yard with it and it ran great. No surging, steady RPMs. Checked the oil, and level, color, and consistency looked good.Took it to my niece's place and mowed her front yard with 9" grass. Ran great. Governor did it's job. Steady RPMs, mower didn't bog down anymore than would be expected when the grass clipping bog down the deck. Checked the oil, and looked as if maybe it was getting thinned out and ugly looking. Wondering if gas is still getting in there. I told her to keep using it for now. Should mention she has a pretty steep side hill in one area of her front yard and I did mow it horizontally, not vertically.

How concerned should I be about gas getting into the oil?

Appreciate the help.

 

[Nessuno]

Would like to add, the mower starts easily when cold and when warm. No smoke out of the exhaust either.

 

[dougand3]

Did NOT put in new diaphragm

I'd do that next. But it seems like a diaphragm stiffening would move less fuel - so puzzling. Maybe tank is heating up in the sun, pressurizing and spitting fuel into intake.

 

[Richard Milhous]

Could water get in the oil? "was sitting outside for a couple of years". Yes, I think it could.

 

[Nessuno]

Maybe I'm overreacting. I did check the oil after running it, so it makes sense that the dip-stick tube might have oil all inside it from running it causing an erroneous reading. They say you should check the oil before a cold start, so maybe I should just sit tight and wait a couple of weeks then check it again. My real question was, on that type of carburetor, in what ways is it possible for gas to get into the oil?

It's not surging, in fact it is running great. So I don't want to replace the diaphragm unless that could be the gas-in-oil culprit.

 

[Richard Milhous]

Sat outside for years, starts easily, runs great.

*SULK*

 

[slomo]

Ethanol fuel, sitting outside with large temp swings daily? Say early spring it's 40F in the morning and 85 in the evening? Yup water is a coming.

Should mention she has a pretty steep side hill in one area of her front yard and I did mow it horizontally, not vertically.

Yup at steep angles gas can/will get into the oil.

How concerned should I be about gas getting into the oil?

VERY.

Pull the oil dipstick and smell for fuel.

 

[Nessuno]

Ethanol fuel, sitting outside with large temp swings daily? Say early spring it's 40F in the morning and 85 in the evening? Yup water is a coming.

Yup at steep angles gas can/will get into the oil.


VERY.

Pull the oil dipstick and smell for fuel.

I know that 4-cycle engines have a tough time on side hills because they use splash lubrication (some might have an oil pump) whereas 2-cycle engines have the oil/gas mixed together. I also know that if you tip the mower to the wrong side that oil can run into the carb/air cleaner, and on this particular type of machine, with the carb on top of the gas tank, I can see where oil might even get into the gas if the mower is tipped to the wrong side. But my question still exists: "How does gas get into the oil?"

 

[slomo]

"Most" splash lubed push mowers are not meant to cut anything over 15-20 degrees. This is a splasher. Long story short, splashers are for mostly flat ground.

Ski slopes require a full pressure lube or similar engine.

 

[Nessuno]

"Most" splash lubed push mowers are not meant to cut anything over 15-20 degrees. This is a splasher. Long story short, splashers are for mostly flat ground.

Ski slopes require a full pressure lube or similar engine.

Yes, I know that. But it still doesn't answer the question.