Fuel Pressure

[CamelToeJoe]

What psi should the pump on an auxiliary gas tank be.  Basically we have an external tank that fits in a hard saddle bag that can be swapped between Valks.  Just trying to figure out the pressure so as to get the correct pump.

Thanks

[Robert]

Figure around 3 to 5 psi is ok if it pumps to the carbs.

[CamelToeJoe]

That's the pressure the fuel pump is we are using and it kills the motor.. Switch to the tank and it runs fine.  A puddle of fuel will end up on the floor. Like it's blowing past the needle valves..

[Gavin_Sons]

That's the pressure the fuel pump is we are using and it kills the motor.. Switch to the tank and it runs fine.  A puddle of fuel will end up on the floor. Like it's blowing past the needle valves..

Hook a hose and a pressure gauge to the aux tank and let it hang low as though it's going into the carbs. This should give you a pretty accurate reading.  I would say 1 psi would get the job done.  You are probably over flowing the bowls and it is leaking out of the bowl vents.

[WintrSol]

Just for reference, pressure of a liquid is ~.4psi per foot of height. The top of the fuel tank on my Tourer is about 1 foot above the carb inlet, so peak pressure when the tank is full is ~.4psi; as the reserve runs out it will be less than .2psi.

[Robert]

That's the pressure the fuel pump is we are using and it kills the motor.. Switch to the tank and it runs fine.  A puddle of fuel will end up on the floor. Like it's blowing past the needle valves..

Yup that is probably exactly what is happening. That is part of the dreaded hydrolock the other part is the tank valve needs to be bad. I have the belly tank and fuel pressure is around 2 to 4 psi and it works fine. The needle and seats along with floats are no different just because they were created to be a gravity feed carb. They should be able to easily stand 3 to 5 psi and keep a proper level. I would just make sure that is the pressure you actually have. This is another reason I like the belly tank, I have a real fuel filter in line and all the sediment goes to the bottom tank and the pump intake also has a fuel filter. The inconsistent fuel flow created by bad needles and seats is sucked into the engine with only minor symptoms on a gravity feed. But under pressure its many times more noticeable, just the same as a faucet under pressure or just siphon feed after you turn the water off.

I have had much trouble finding an aftermarket pump that has low pressure and high flow you may want to make sure your pump is running the correct pressure.

Below is the Facet pump chart the one is used for the belly tank are listed at 1 to 4 psi. I dont remember the number that is used because the one that is used has one more valve in it.  It has a anti siphon valve as well as a anti drain back valve and works quite well. These are very simple pumps with only one real moving part. A plunger in a cylinder that moves back and forth with a check valve in the cylinder. You could try one of these or if your interested I could try to find the number of the pump I have on mine that does fine. If you decide to get one of these pumps do not buy it from Advanced or other parts stores before you make sure its not a Chinese knock off. They are terrible compared to the Facet pumps and I have had problems with them. They look the same but they dont work the same.

http://www.facet-purolator.com/cube-fuel-pumps.php

[WintrSol]

I have had much trouble finding an aftermarket pump that has low pressure and high flow you may want to make sure your pump is running the correct pressure.

I don't think high flow is an important requirement. Say you get 25mpg at 120mph, that means you are using 4.8gph, or 0.08gpm. Many pumps can provide that with ease.

I agree, though, that there shouldn't be an issue with 2-5psi leaking past the float valves; my VS800 has a pump, which is not rated for pressure, but has been measured between 1 and 2 psi before shutting off, and I've never had an issue with over-filling. Perhaps the OP should get a pump for the Suzuki - it's fairly simple, and could be easily wired into the system; it shuts off when the pressure reaches a fairly low set point, and won't run again unless the engine is running.

[CamelToeJoe]

Thanks for the replies.