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Discussion Starter · #1 ·
Cleaning up a complete and stock 10 year barn find..

I've just disassembled and cleaned the 4 kei-hin carbs on a customers 1998 ZX600E and although the bike starts and runs fine through the entire throttle range from a gravity feed fuel bottle, when I connect the fuel pump and new filter it floods within 20 seconds at idle or even off idle. The revs slow down, sputters, and falls on its face. Plugs wet. Cleaned plugs, go back to bottle fed and it runs fine with no flooding.

Instinct tells me to check the psi from the pump, but I'm not sure I have a gasoline compatible pressure guage. Is the pump overwhelming the float valves in the carb bowls? Is the pump supposed to shut off when it senses back pressure?

An old thread on a different forum suggested the CDI/ecu might be holding old info from clogged fuel filter and calling the pump to put out a hight pressure than necessary - remedied by disconnecting battery for a while to clear "codes". But that didnt fix it and thatinfo might be very incorrect.

I really don't want to have to take these carbs off again.

Tia for any suggestions.

I didn't change or replace any interior carb components or readjust the float height on any of them. Again.. runs fine with gravity feed.
 

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The fuel pump is not ECU-controlled. It should have a self-limiting system where it shuts itself off once the correct pressure is reached.

I think your thoughts on this are mostly on the right track. Either the pump is putting out too much pressure or the float/needle valves aren’t closing tight enough.

An easy check of the fuel pump is to bypass the fuel pump relay so you can run it without cranking/running the engine (so you can easily hear the pump operating). Turn the pump on and listen, to hear if it stops when the carb float bowls are filled. Maybe drain those float bowls first so you can hear the pump run as needed, then stop when they’re full.

You could certainly check the fuel pressure with any ordinary pressure gauge but I don’t know what the correct pressure is.

Good luck
 

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Discussion Starter · #4 ·
Below is how to check the fuel pump on the ZX6E. The pump has a built-in pressure switch that stops it from working when it senses a little back pressure.
This is excellent info sext-ah.. sexy sexsex..
I'll try to attach a video but short story is that with the testing fuel lines filled and deadheaded, the pump pressurized the system to ~160mm/Hg which is equal to about 3.0psi and then shut itself off. It wouldn't run again until some pressure was relieved and then it satisfied itself again, and stopped.
I used a Powerprobe to activate the pump so I could hear it run and stop.

This saved me the cost of an unneeded fuel pump and taught me a little about these things.
Unfortunately, now it's back to carb tweeking.

I just didn't think that carb floats could handle anything more than gravity pressure from the fuel in the tank and thought a pump would overwhelm them and overfill the bowl.
 
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