Bob's Guides | Leaking Generator Fuel Filter I learned something recently about Onan generator fuel filters — sometimes they leak! After changing the oil, oil filter, and air filter on my Onan generator, a ran it for a bit with the cover off to make sure the oil filter wasn't leaking. Onan fuel filter leak - Kawasaki Teryx Forum Jun 20, 2012Onan fuel filter leak. So I picked up a new trailer the other day and was giving it a once over at home. I smelled gas in the generator (Onan Marquis 5500) compartment and finally found that the culprit. The fuel filter that screws into the carb was leaking, at first I thought it was at the threads but it wasat the crimp/seam.Author: UTV Inc.