downward fuel filters

[XS1100_OEM4ME]

OK, some have heard of my carb gas problems. What if I turned the fuel intake "t's" downward, then hooked up the fuel filters below the bowls, then plumbed them to the octy, then to the petcocks. Do you think that would fix the gas from running out of them and overflowing the carbs

[DGXSER]

Fluids will always seek their own level. So, if you have an open system which our fuel systems are until you close the petcock and ti seals or the octy seals off, the fluid will flow down until the carb valve closes off, or the fuel in the inlet tubing system is at or below the inlet of the bell of the carb, where it is flowing out, if the float valve fails.

Now, once you seal off the path for air to fill the tubing behind the fuel, it will stop flowing, no matter what height and such is there. We have all performed the thumb over the end of a straw trick with your coke at McDonalds or whatever. And if the fuel valve in the float bowl seals it will stop the flow coming in based upon pressure to the floats from the rising fuel level. Yes I know this is not news to most of the folks here including you OEM.

So, you can extend the fuel lines down as low as you want, and still, the fuel above will drain down, through any filters you have in place no matter where the filter is. That is my prediction anyway. I doubt those fuel filters offer enough restriction to hold back any real height of fuel behind them.

[Rasputin]

DGXSER has it right. The only thing that may differ is the operator. Fluid will self level even at 5 or 6 thousand feet. I worked rigs years ago and used that to my advantage while swabbing the well.

[XS1100_OEM4ME]

+1

+1, any fuel ABOVE the bowl's will drain down into the bowls with any leaking from the needles, my point is the filters hold a couple of OZ's of gas, the lines, not so much, so if the filters are below the bowls, they will not add there extra load of gas to the bowls while sitting

Fluids will always seek their own level. So, if you have an open system which our fuel systems are until you close the petcock and ti seals or the octy seals off, the fluid will flow down until the carb valve closes off, or the fuel in the inlet tubing system is at or below the inlet of the bell of the carb, where it is flowing out, if the float valve fails.

Now, once you seal off the path for air to fill the tubing behind the fuel, it will stop flowing, no matter what height and such is there. We have all performed the thumb over the end of a straw trick with your coke at McDonalds or whatever. And if the fuel valve in the float bowl seals it will stop the flow coming in based upon pressure to the floats from the rising fuel level. Yes I know this is not news to most of the folks here including you OEM.

So, you can extend the fuel lines down as low as you want, and still, the fuel above will drain down, through any filters you have in place no matter where the filter is. That is my prediction anyway. I doubt those fuel filters offer enough restriction to hold back any real height of fuel behind them.

[DAVINCI]

Fix the carbs

[TADracer]

Here is a thought (Geez, he's thinking again).

Considering that everything is right in your carbs, how do you have your bowl vents plumbed? Try sending a piece of hose from the vent tee as high up under the tank as you can and see if that helps.

I had the same problem when I first switched to my ZRX carbs. The bowl vent is in about the same location as the Mikuni's. I could turn on my petcocks and fuel would run out of the carb bells. When I raised the vent tube up into the tunnel under the tank, all leaking stopped. Still have not figured it out but, I have not leaked even a drop since. Worth a try.

[old_skool]

wouldn't the floats either have to be leaking or improperly set to leak from the vents?

[DGXSER]

Under Pressure (dum dum dum dumdumdum dum)

Yeah, think Queen (or Vanilla Ice)...

Ok back to carb stuff, its all about pressure. The fuel sitting in the tank exerts pressure to push fuel out the through the petcocks, and tubes, filters, OCtY, Tees and the fuel float valve into the carb bowl. At some point, the float begins to....well....float, and it exerts pressure on the float needle valve to push it into its seat. when the pressure exerted by the float on the needle valve exceeds the pressure of the gas pushing down from the tank through those tubes and such, the fuel stops flowing. I know, basic stuff for most folks here. It just helps me to think it all through. when we set the float height, essentially, we determine or change at what level of fuel those two pressures meet and then the float pressure exceeds the fuel pressure.

Here is where it gets tricky, the vent has to let the air out of the carb bowl for the fuel to displace it, if the vent does not let the air out, then the air trapped at the top gets compressed by the incoming fuel, and pushes back, in some ways helping to stop the flow of fuel, but it also pushes against the rising floats to stop them from putting pressure on that needle valve to stop the gas from coming in. So the float does not rise up, fuel keeps pushing its way in, and now the fuel in the bowl is under higher pressure so it finds the path through the mains and the emulsion tube, or the other paths to the main carb air passage. Paths it normally needs engine vacuum to pull it through, it is getting pushed through by the increased pressure in the bowl.

So as strange as it may sound, a lack of path for air to escape the bowl lets more fuel in.

[TADracer]

wouldn't the floats either have to be leaking or improperly set to leak from the vents?

Yeah, I figured that too but these are 2001 carbs with new viton valves and seats and the floats are clear plastic, not brass or a composition. I set the fuel level (not the float height) with the rack-o-carbs in a jig on a level bench at the factory specification for the carbs.

Only thing I could figure jives with what DGXSER said. When I set the fuel levels I used a 1 quart can to feed the fuel. Maybe the weight of a full tank makes a difference. I do not know but all I can say is it has not leaked a drop in two years.

[BA80]

One more time.

If the carb floats and valves are correct you shouldn't even have to worry about the petcocks or the octy. I ran mine all the way up and back from Minnesota last summer on prime and never shut them off.

[XS1100_OEM4ME]

Helpful

Thanks, that is helpful, after reading it a couple of times, it got me thinking, even if my airbox vents are clear, if even one of the carb vents is not clear, as fuel bleads down after shout off, the air pressure in the carb would force the fuel up and out the carb, instead off just a slight rise in the bowl I will check ALL the lines and "T's" to make sure there is no restriction Thanks

Yeah, think Queen (or Vanilla Ice)...

Ok back to carb stuff, its all about pressure. The fuel sitting in the tank exerts pressure to push fuel out the through the petcocks, and tubes, filters, OCtY, Tees and the fuel float valve into the carb bowl. At some point, the float begins to....well....float, and it exerts pressure on the float needle valve to push it into its seat. when the pressure exerted by the float on the needle valve exceeds the pressure of the gas pushing down from the tank through those tubes and such, the fuel stops flowing. I know, basic stuff for most folks here. It just helps me to think it all through. when we set the float height, essentially, we determine or change at what level of fuel those two pressures meet and then the float pressure exceeds the fuel pressure.

Here is where it gets tricky, the vent has to let the air out of the carb bowl for the fuel to displace it, if the vent does not let the air out, then the air trapped at the top gets compressed by the incoming fuel, and pushes back, in some ways helping to stop the flow of fuel, but it also pushes against the rising floats to stop them from putting pressure on that needle valve to stop the gas from coming in. So the float does not rise up, fuel keeps pushing its way in, and now the fuel in the bowl is under higher pressure so it finds the path through the mains and the emulsion tube, or the other paths to the main carb air passage. Paths it normally needs engine vacuum to pull it through, it is getting pushed through by the increased pressure in the bowl.

So as strange as it may sound, a lack of path for air to escape the bowl lets more fuel in.

[kwats]

Something worth mentioning....

Last year the gas cap vent was plugged on my special. Heat from the motor caused some pressure in the tank while setting after a ride, especially if the tank was 1/2 full or less. I had the viton float valves in at the time, and I got some fuel past the valves. Since then, the octy has been launched, the ports on the petcocks have been epoxied shut, the viton float valves have been replaced by stock, and the tank vent cleared. I have gone back to my old habit of shutting off the petcocks whenever I shut down as I have done for 45 years. Yamaha did not do anyone but their liability insurance carrier any favors with this design.
I like the bike, but any more fuel issues will cause me to pull the tank and fit it with some high quality Pingle petcocks.