My new Briggs push mower started running rich, smoking black. Had only been used maybe 5 hrs over 2 years. Stored in outdoor shed and kept dry. Used plain gas, not E10. Foam air filter was clean on the inside but the circular airflow ports in the filter housing were completely gummed up with black almost plastic-like gunk after only such short usage. In the past, air filter foam elements were oiled with regular oil and dirt particles grew like hairs or filings on a magnet. Even really dirty, air could still be sucked through. With this new oil, it gums up and nearly solidifies. Cleaning the housing and filter felt like wiping off very thick KY jelly. The owners manual says to clean the filter with detergent and water, not solvents, so I assume the "new-improved" air filter oil is water-based. In my case, I think it was hydroscopic, trapped water and dirt, solidified , and made a plastic -like paste that was impermeable to airflow. Another case of "save the planet" , but create a worse product than the original.
I have never changed the type of oil I use on air cleaners. Still use 30W, same as I did 30 year ago. Never had a problem. Just squeeze it as hard as you can. Dawn dish soap and warm water have always been the best cleaner for me.
