So I was doing an oil change yesterday and while draining the swingarm, I heard a constant bubbling sound. I traced it, as best as I can tell, to the fuel pump area. It seemed like a steady sound of air leaking into the tank but there was no sign of any fuel trading places with it.

I searched the forum and only came across one other post asking a similar question and relating it potentially to a faulty fuel pressure regulator but there were no replies to it. I can understand if the regulator is failing to hold pressure and bleeding it back into the tank, but that shouldn't result in air being introduced into the system. I thought one option may be the tank vent valve being blocked causing a vacuum in the tank, but I tested the drain line and its clear (got a nice little octane buzz in the process ).

My bike is a little stumbly around the 3000 RPM range but I have some troubleshooting planned to address that, just in case that may be connected.

Any thoughts from the experts?


Extra details:
2008 XB12ss
12,000'ish miles
K&N filter
Stock Exhaust & ECM
94 octane (Ethanol free)