great post dave!
i learned several things. perhaps i would be better to just block off the l/8" fuel line from the vent to the fuel tank. everything is running just fine and i can get the air out of the filter buy taking out the event plug if i ever need to. unless you see this as a mistake, it seems that this will be my best option. and thanks again dave. i really learned from your post. mark
Mark
I have been looking for a fuel filter system descriptive diagram to help both of us understand what Kubota's design is trying to accomplish but have had no success.
Lets review what might happen if the extra line is attached to the vent. Possibly not enough fuel to feed the injection pump.
If the line is not attached, then the possibility of air getting into the injection system and stopping the motor. This would be a good time to review the injection system bleeding procedure for your tractor so you are prepared should something go wrong.
Conducting some experiments with the extra line might give you useful into. Attach a small funnel to the filter end of the extra line and see how quickly or slowly the line will let a fluid, i.e. diesel flow into the tank.
If fuel flows quickly through the line then clearly, if there is a restriction as I suspect, it must be in the filer housing itself. You may be able to see the small orifice if you look both inside the housing and down into the port from the outside.
Lastly, make a test rig where you can flow diesel through the original filter. A long rubber hose and a funnel 18" above the filter housing would simulate the pump delivering fuel to the filter. Now you can see how much liquid comes out the line to the injection pump compared to the third line.
On a much earlier generation of tractors, there would be two filters side by side with metal sided replaceable cartridges. On the top of each filter housing there was a banjo bolt which led to the fuel tank. On the filter closest to the fuel tank the banjo bolt securing the fitting had a .030 orifice to restrict flow. On the first filter in the line, there was no restriction. Lastly, the line venting the filters extended to the bottom of the fuel tank. Over the years, this line would fail and fall to the bottom of the fuel tank. There was no external leak to indicate a problem. However, the owner would start experiencing air problems and have to be constantly bleeding the injection system. The design anticipated fuel cooling down when the engine was stopped and the vent line to the bottom of the fuel tank drew fuel back through the vent line keeping the system air free. When the vent line was above the fuel level in the tank because the line had broken off inside the tank, now air was drawn back into the system.
A lot of rambling on to try and show systems are often more complicated then they look.
Dave M7040
