I don't know if it's consuming oil. I don't use it enough to know, and I've been changing the oil a lot due to the problem it had with gas getting into the oil. I think maybe I still have that problem and need to service the carburetor more than just installing the shutoff valve.
It should be a pushrod engine (easy to take the head on and off), but I agree with the others that you should leave the head on for now- there's nothing under there that can be easily serviced and the carb will be the simplest place to start.
If you think that it is flooding while parked, then you can splice a fuel shut off valve into the line and always turn it off when it is not running.
Dirt in the float valve will cause it to flood while sitting and running- which would explain the smoke.
Does it have plenty of power and run smoothly? Or does is cough and sputter and puff out black smoke when mowing high grass? (sign of flooding/running rich)
Perhaps your overfull, gasoline thinned oil slipped past the rings and fouled the spark plug.
Most lawn mower shops will sell you the float valve needle, you just need to give them all of the part/serial numbers off the engine cover.
To inspect the needle, you will need to remove the float- just pull out the nail looking shaft that the float pivots on with needle nosed pliers and then the needle will likely fall out. On most small engines, you don't necessarily have to take the carb off to clean it (leaving it on will save you the hassle of disconnecting/reconnecting the throttle/choke linkage).
Once the needle is out, blow carb cleaner through the carb fuel inlet and inspect the tip of the needle. Adding a gas line filter/replacing the one that is on there will help to prevent future problems.
Also shake the float to check that it is not filling with gasoline and sinking.
I have spliced in the fuel shutoff valve, almost a year ago.
It does have plenty of power and runs smoothly. It might stumble a bit when it emits a particularly strong puff of smoke when I'm facing downhill.
I'll have to get a carburetor book from the library, they've got plenty. Then I can check the float valve and (as suggested on another forum) replace the "needle and seat". Would that be the same as the float valve needle?
How would I know on visual inspection if the needle is good?
I do have a filter, it's between the shutoff valve and the carburetor.
Other info: I've had the carb off a few times to soak it in carb cleaner after leaving gas in it all winter and that gas turning into varnish in the carb. Once I had a hard time with it and really got abusive with it, trying to force aerosol carb cleaner through passages.
I wonder if I need to try to rebuild the carb or get a replacement.
I wonder if I could just stick a diesel particulate filter on it and it would filter out the smoke and then I could just ignore it until it catches fire again.
Well, I took of the carburetor and put everything else back together.
The float didn't have any gas in it, I'll try to sink it in some water and see if it bubbles or floats.
The whole carburetor has quite a bit of [mostly green] corrosion in it, surprisingly. I've never seen corrosion in it before, just varnished gas. A thing that I'm pretty sure is the float valve needle is corroded, for example.
I borrowed a few books from the library, one of which has full color pictures and if they didn't use my engine for the carburetor section they used a very similar one. Unlike most other small engine repair books in the library, this one appears to be from this millenium. I think it was published in 2003. http://www.amazon.com/Small-Engine-R.../dp/158923121X
The photos of the carburetor look exactly like mine.
I'll probably post a new thread with pictures of my carburetor. This thread is a mess.