TOPIC:

My voyager recently developed a frustrating problem, I'm looking for tips on diagnosing it rather than just start throwing parts at it. I haven't mounted a gauge yet, but I am pretty sure I'm losing fuel pressure at WOT in the upper rpm range.

The bike will bog out, and catch back on after a few seconds and bog out again, so on and so forth. The pump doesn't really sound healthy, but neither have the others ive heard, judging by youtube videos. Its also only started doing it recently, no change in the pump sound.

Fuel filter is new, tank is clean and petcock clean. Tank check valve clean and working. Fuel flows freely from the tank and into the filter.

Partial throttle operation and normal riding the bike runs excellent, it only starves under WOT.

Should air be in the top of the fuel filter? Or should it be constantly full of fuel? Mine always has 1/4-1/2" of air in the top when its running

I'm not sure if I should replace the fuel pump at this point, or the pressure regulator. Is there a good way to determine what is at fault?

You would need to put a pressure gauge into the system after the filter and before the fuel rail and check it at various speeds and throttle settings to get a good idea of where to look. Fuel pressure regulator would my first port of call but a gauge is necessary to do an acurate diagnosis.

Hooking a gauge up is the next step, though I'm relatively certain that it is a low fuel pressure problem. I'm just wondering what would cause it at this point.

Do the pumps have a tendency to get weak? It doesn't sound like a car pump when I turn the key on, it sort of grinds and has a nasty gurgly sound to it. This leads me to believe my pump may be biting the dust, I wish I had a way to bench flow test it.

It will be a rolla cell type pump which should be fairly quiet so if it's noisy then it's a good bet it is probably shagged. Don't go out and start looking for a genuine unless Bill Gates is your uncle. AFAIK the Kawasaki DFI is fairly much a knock off of a early Bosch LE-Jetronic system which runs at 2.5bar so almost any pump will do the job. The outside diameter and whether it's an internal or external pump are the governing factors. Most from that era are 52mm so you have a good choice. If you go to fleabay the pictures will give you a good idea of the outlet and configuration of the filter and connections. You should be able to get one for around $40 US.

It seems to be the same pump that the old GPZ 750 turbo and GPZ1100s used, which according to their forums is the same as an early GM fuel injection pump. They aren't too expensive, I guess I'll get one on order