K&N has filter cleaner and filter oil designed just for that application, use the stuff for years on aircraft.Thanks for the reply Budegan the filter is washed and drying I have the oil I need so I'am just about there .
Ted's right, WD40 is a poor choice since it rapidly evaporates leaving little oil behind. If you can find some K&N or other air filter oil, it's a little different in that it's more sticky and doesn't dry out as fast. You can clean the filter with solvents, gasoline will work but be careful, paint thinner is also okay. I don't know about more aggressive solvents like acetone, MEK and such, they may attack the foam.It's better to use the right stuff. WD40 is okay in a push, but really isn't suitable for long term use.
I used K&N filters on ultralight aircraft for quite a few years. I always cleaned and oiled them with K&N's cleaner and filter oil.I have used both the K&N and the oiled foam type of air filters. It is my understanding that they are quite different from each other.
K&N uses a thin oil to moisten a thin filter membrane. The foam filters use a very thick, sticky oil to coat all the foam cells throughout the thickness of the filter. Very thick gear oil is suggested for this if the proprietary stuff is not available.
The foam filters are regarded as doing a better job of filtering particles out of the air than K&N.