Generator pulsates when its running 12-KW natural...

Question

Generator pulsates during running and the lights in the house also. Also seems to be oil in the air cleaner area. I' have to shut it down after 10-12 hrs. to check the oil and most of the time add oil. The dip stick is really hard to read also is there a trick to being able to see the oil on the stick a litter eaiser.