I've got a question for yall. I've rebuilt the carbs and got everything cleaned up and put back to spec. The issue I'm having is that when I gravity feed from the tank to the carbs the bike runs and holds idle but when it's hooked up to the fuel pump it floods the bike out within a minute. One of the shops here in town is saying I need a new fuel pump. That there is something inside the fuel pump that when it goes bad it will dump fuel instead of feeding the correct amount. Does this sound right? Been throwing parts at her for months now and it's getting to be more than a little expensive. Any advice would be greatly appreciated. Thanks

 

that doesnt sound right. the floats and float needles are what regulate the fuel level in the bowls. gravity feeding fuel will produce less pressure than the pump, so introducing the pump may be enough pressure to leak past the float needles if they are not sealing properly. have you rebuilt your carburetors recently?

 

I don't know about the f4, but in the f3 service manual there is a test you can perform that actually measures the amount of fuel supplied from the fuel pump. There is an acceptable range. Knowing if the fuel delivered is within that range is a great first step in troubleshooting. Even if the f4 manual doesn't have that, you could use the f3 steps. The range should be pretty close. There is a .pdf version of the service manual in sticky section of the f3 forum.

 

If I remember correctly the fuel pump is not meant to be constant duty - it cycles on and off. Yours might be stuck on?

 

there is a procedure in the manual for this test for the F4.

Disconnect fuel line from tee connections at the carburetor
put hose in container (they say beaker)
turn on ignition so fuel flows into container for 5 seconds
multiply amount of fuel collected by 12

should be 23.7 oz of fuel

 

It's the same pump across all the models - so you are correct the flow should be in the same spec. I am more worried that it's stuck permanently on?

 

Pump relay is triggered by ignition pulses. At idle, there's fewer pulses per second and less fuel pumped. At higher revs, more pulses per second and more fuel pumped to match demands. Make sure wiring is connected properly. Pump should not be on full-time and it only pumps when engine is spinning.

 

even if the pump is stuck on, it shouldn't cause this problem. the pump should not have enough pressure to overcome the floats. otherwise, you would flood the engine by turning the key on and off rapidly.

 

It very well may be.
Question. On the f4, does the fuel pump come on when you turn the key to the on position? It does not on the f3. To perform the test on the f3, you have to jumper two wires together. I actually do this when I'm reinstalling a set of carbs so that it primes the cabrs with fuel, so to speak.

 

the F4 does have a priming function when key is turned to the on position. if you cycle the key a few times, you can hear the fuel system build pressure to the point that the pump can no longer pump. which is why I believe this to be an issue with the floats and/or float needles.