How to determine faulty Fuel Pump

While the rear cowl was off, and my bike was finally running again, I noticed that the fuel pump was really loud. I put my hand on it, and it was vibrating pretty hard, not a quick vibration, either, a low frequency vibe.

I have noticed that sometimes the bike is a little chuggy at higher RPMs - could this be the culprit?

 

Should be a fuel pump flow test in the manual...

 

I saw the flow test, just have not performed it yet.

The thing that concerned me the most is how quiet it was jsut after you turn on the key (but bike is not running). It does not make any noise. It isn't until the bike is running that you can see it visibly vibrating (not from themotor running), and if you put your hand on it, it feels like there's something "out of balance" inside the pump.

I did run the bowls out of gas when I took the tank off to re-tape the wire harness after my R/R wiring upgrade. The fuel pump did sound like it was working hard. It was not cutting out at all.

BTW - how do the float valves "tell" the fuel pump to regulate the fuel flow to the bowls (to prevent flooding)?

 

Guys, would a clogged fuel filter have similar symptoms?

 

PB's guess follow-up... is there an obstructions between the pump and the intake? Such as.. clogged fuel filter, kinked hose, ... etc.

Flow Test should help.

 

The pumps have a backflow sensor.

So as the gas in the float bowl rises, the float closes the float valve - not allowing anymore gas into the float bowl. When all 4 float valves close, the pump senses the backflow and shuts off. If you have a kink, or a fuel filter between the pump and the carbs, the pump may sense false backflow pressure and shut off too early.

 

So the vibration in the pump is the symptom (sp?)

The cause would seem to be the pump is
a) looser that it used to be in its mount
b) working harder than it used to
c) not working as well
d) some combination of a,b,c

a would likely be caused by b or c, so let's look at them.

b - working harder due to internal pump friction, internal wear causing it to be out of balance, or increased back pressure. Only increased back pressure can be corrected w/o a new pump.

c- this can only be fixed with a new pump

d - back to new pump or increased back pressure.

eliminate the possible presence of the back pressure by the flow test, if the flow test passes, and the pump vibrates during the test, replace the pump.

Does that make sense to the causual observer?