There is oil leaking into the air filter on my garden cultivator

replace the air filter(clean air filters are most important)
use a heavier grade oil
make sure that the fuel is leaking past the needle and seat when not in use and diluting the sump oil

could be from a sump problem and blowing oil out of the air filter inlet hose

1. Make sure that the air filter for the carburetor is clean/dirt-free; If not, clean with some gasoline, squeeze out the excess gas, replace and try starting.
2. Check to see if there is too much oil in the sump (the place where oil lives in your machine!) Too much oil may cause machine to slow down or stop. If the oil supply expands it can thwart motion of the parts it lubricates. Check to see if the oil level is above the 'full' line. If it is, drain some (but not in the garden soil!).
3. Another possibility is that the spark plug is fouled; look for oil at the spark gap. If there is no sign oil, clean/replace plug after checking the gap, reinstall plug (no more than a quarter turn more than finger tight) and try again.
4. Ask your mother!

How does it run? Is it back firing through the air filter box area? And although your stating it is oil is it actually oil or gasoline that is black due to getting dirty? Don't shoot me! I'm going on what information I'm reading what you submitted. If oil is it enough to show up quickly on the dipstick/engine oil level ? Get back to us and we can go further.

what engine is it?

Hi, Check the oil reservoir breather that it's not plugged up. The oil should be returning back to the reservoir not going to the filter. That tells me that there is air being pumped into the engine (oil).
The piston rings could be broken or the carberator needs to be readjusted.

Open the air screw abit more on carb. Then see what happens. Good luck.

overfull dip s or mower tilted the wrong way allowing sump oil to flow out of the breather tube into the air filterump

If the tiller was lying on it`s side the oil would flow into the carb. and filter.
You will have to remove the carb. and wash it out. Check there is not too much oil in the engine.

Oil normally comes out of the air filter area a little bit, but over time, once the oil rings start to wear, more and more oil comes out. So you can either have new oil rings replaced, or you can put in a crank ventillation valve in there and it often helps slow down the oil from entering

the oil filter is either cross theaded or the filter is not tite enough