I inadvertently overfilled the engine oil and ran it. It is a Kohler 12.5. It started to blow smoke out of the exhaust and I noticed oil in the carburetor. I drained the oil and noticed that there was a smell of gas in the oil. Replaced the oil and cleaned out the carburetor and I also took valve cover off and cleaned the reed valve, then reinstalled the cover. Before I try to restart the engine any thoughts on if this is the fix or is it more than likely something else?

If you put too much oil in it, this is usually what will happen. Based on what you have said you did, you should be OK now. You might have some residue that will burn off but you should be good to go.

Just started tractor up and it ran for about a minute then same problem, this time I disconnected the breather tube and started it up again and a mixture of gas/oil came out of the valve cover where I disconnected the breather tube. I checked the oil and drained it. There was more gas than oil in the crankcase, what's my next step?

Sounds like right now the carb needs to be cleaned... like the float is sticking or something along those lines. Beyond that, I can't really say for sure. I would start there though.

Seems odd that carb could have started leaking in conjunction with my adding too much oil...

My guess is that the oil got into the carb and stuck the float or clogged the needle. Gas is coming from somewhere and stuck floats and clogged needles are the main cause.

I also saw somewhere that if oil get into gas pump it could cause a similar problem... any thoughts on that?

Traditionally, tipping the mower too much to the side or overfilling the crankcase will cause oil to be sucked into the oil breather tube, which will be burned and produce lots of smoke. If you can, just run the engine until the smoke stops. Ensure the engine oil is not overfilled and that the oil breather tube is connected.

Tried replacing the needle jet in the carb, but after I did this I changed the oil and filter and then started to cut grass. Tractor worked fine for about 30-60min and started blowing some smoke out of the exhaust. It is sucking it through breather into carb, no doubt gas is still getting into oil. How else could gas be getting into oil other than through the carb? The unit was running the whole time so the carb was not leaking into cylinder.

Have you recently cleaned or replaced the air filter?

Yes

I'd be inclined to remove the carburetor, soak in Stoddard fluid, and replace the float's needle valve. Old gas can gum-up and then the float's needle valve can't cutoff the flow of gas to the carburetor. Did you let the mower sit over winter with old gas in the bowl?

I use the tractor all the time and it never gets a chance to sit. I did change the oil and put in new air cleaner and pre-filter, seems this where everything happened. I put in about an oil filter contents too much oil and it went downhill from that point. I noticed smoke belching out the exhaust after I ran it for about 30-60 min, found gas in oil. Changed needle valve, no gum or residue in bowl, rechanged oil filter and oil again. Mowed the grass for about 30-60 min again and it started doing same thing, pulling oil/gas through breather into carb causing it to go through exhaust and smoke. What else could be causing this? Seems it has to be related to the initial oil change/air cleaner replacement or else pure coincidence.

Remove the float's cutoff needle valve and look for hardened gum in the seat. If the cutoff valve is not working properly, excess fuel will flood the crankcase.

Is the carburetor the only way gas can get into crankcase? Can the engine be running and still allow excess fuel into crankcase?

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Originally Posted by mrmcmaple

Is the carburetor the only way gas can get into crankcase? Can the engine be running and still allow excess fuel into crankcase?

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If it has bad piston rings this could happen as well. Considering it wasn't happening before, it doesn't seem likely that bad rings would be a cause.

I am noticing a small drop every second or so coming out of the breather tube, must be oil. Would this indicate some sort of negative pressure or any other condition that would make it somehow draw gas into the crankcase. I know that excess vapors go through breather tube and that I should not be seeing drops. Any help please... grass is getting taaaalllllll

Just tried an experiment and disconnected breather tube from valve cover... nothing came out of valve cover outlet that tube connects to, but when I connect it to the breather it lets drops out that are gasoline... how is that possible, gas is being drawn into valve cover and that must be how it is getting into crankcase. Any thoughts?