Sounds like high crankcase pressure or heat IMO. Possible reasons and maybe some areas to tests.

1. Too much oil (in level position sitting engine. What is
the “recent” history before this started?

2. Possibly sticking rings or some cylinder wear (Ck
Compression. Age or hrs on the engine?

3. I have not pulled a fill cap on a small eng running but
this on a running car will show high pressure.

4. Could the eng be running hotter due to cooling air restrictions? Have you pull the cover to ck fins.

5. What have you checked?
Have you checked the valve clearances?

Good Luck! Please
share what you find.

A few things to add: The breather itself can be defective. It is a weak link on these. Be sure that there is no presents of fuel in the oil. An over speeding engine will cause a similar effect.

The crankcase breather has drain back oil hole or holes very small they fill sludge cleaning breather good thing install small holes so oil drain.

A pretty white air filter on carburetor help crankcase pressure.

I haven't checked the valve clearance yet, the fins are clean and no obstructions, no idea on hours or history, the oil level is at the full mark with no sign of gasoline I'm using Shell Rotella 5W40 syn. I ran it for an hour and a half today chipping up some branches. It didn't smoke and the oil hasn't gone down. After shutting it down I checked the breather output to the air box and found this

They quit suggesting 40w oil on these many years ago as they would foam. Change the oil to ideally an SAE 30. Use a multigrade if you you must due to the weather, but like a 10W30. I can't tell what the 1st pic is. An LEV 120 has a round breather element under the flywheel. No other filter like material other than the air filter itself. If it isn't using oil , blowing smoke- I wouldn't worry about it.

The old TVS Tecumsehs had that small filter built onto the air filter- like a flap. It is likely there to control any misting that may occur. But when that style breather decides to pump oil, you will know it.

Thanks Tom. Can the breather on these be cleaned or is better to just replace it?

It can be cleaned, but you would want to get the breather kit if you pulled it apart. It does require that you pull the flywheel- and you should have the proper puller to do so. Instructions come in the kit, but certain parts that used to come in the kit are NLA- so one has to use caution. One thing on these are that if the unit gets tipped much past 90 degrees and the breather chamber fills w/ oil- the breather will act like a little pulse oil pump and actively will fill your air filter. You could warm the engine, shut it off and try back flushing w/ mineral spirits through the tube. Then change the oil.