fuel pumps

[JerryS]

Hi I have the carbs off and fuel will run out of one pump and not the other. I had to empty the tank or it would of run out. I was wondering if this is normal. which pump is working right the one fuel runs through or the one it doesn't.

[Mad Powersports]

Which line is it running out of?

If it is the pulse line (to the crankcase) it has a broken diaphram.

[turbogriesbach]

Fuel shouldn't run out, they have a built in check valve.

[JerryS]

It runs out of the fuel lines that go to the bottom of the carbs. That is what I thought I do not remember that I ever had to drain the tank to remove the carbs before. When it sits for any length of time and I start it it fouls 2 plugs I have ordered the "O" rings for the floats but I should also look at the fuel pump that the fuel leaks by on too Thanks I will check that tomorrow.

[mjdevries]

Fuel shouldn't run out, they have a built in check valve.

The check valves simply allow the flow in 1 direction, which would be from the tank to the carbs. There should be 2 of them. The first one would allow fuel to enter the pump when the pulse is negative (vacuum), then this one would be force closed when the pulse goes positive which forces fuel past the next check valve into the second half of the pump, and the cycle is repeated.

If these check valves are stiff enough they should limit the flow, but I cannot see them necessarily stopping it all together. One other reason that you might not see any gas coming out of the other pump would be that there could be and small air leak in the line from the tank to that pump. This would break the siphon that is necessary to keep the gas flowing from the tank to the fuel pump.

The fuller the fuel tank the more likely it would be that the fuel would flow past the check valves as you would have a larger difference in the height of the top of the fuel in the tank with the fuel pumps which once siphoning starts would put more pressure on the siphon line.

I would however recommend pulling both pumps out to while you have it open and check them out. There isn't much too them, but you could have something in the one that is flowing that is holding one of the check valves open, and the other one could have some build up that is keeping them stuck closed. Either case would not be good.

In the mean time. If you want to break the siphon, pull the spring around the black rubber lid where the fuel lines go into the tank and lift the lines out of the tank and inspect the fuel filter. This will break the siphoning and stop the fuel from flowing while you work on the pumps and carbs.

[Mad Powersports]

All of the above plus, Make sure your vent line isn't plugged.

Thats a common scenerio when someine brings the sled into a warm area and it start leaking, as fuel warms it will pressurize the tank and if the vent is pluggued it will push it out where ever it can.

Although this type of problem usually is accompanied with a driveability issue.

Just something to remember.