fuel tap

[Morala]

Hi, on my 74 550 i have i believe an original fuel tap with two outlets, it may be a silly question but should the fuel be coming through the both outlets as mine is only running through one even if i put it on reserve position.any advice very welcome.

[Johnwebley]

Hi, on my 74 550 i have i believe an original fuel tap with two outlets, it may be a silly question but should the fuel be coming through the both outlets as mine is only running through one even if i put it on reserve position.any advice very welcome.

The fuel will always find the easiest path,

To test it

Block the outlet that is flowing,

It should then flow from the other

Sent from my SM-A546E using Tapatalk

[Bryanj]

Both should flow on normal and reserve, as said block the one that flows and see if fuel flows from the other

[Morala]

thanks guys for your replys, i removed the fuel tap to check if everything was ok, inlet was clear and so were the outlets filter was good so tried what you suggested and closed the outlet that was running and the fuel ran through the other outlet, i thought you needed both outlets running to feed the carbs but i have never had a 4 carb bike before so still learning thanks again for your help.

[Bryanj]

Fuel is like water and electrickery it will take the path of least resistance, when the 2 carbs fed by one pipe fill up the others start, when all full flow evens

[Morala]

thanks Bryanj makes sense now

[Sesman]

thanks Bryanj makes sense now

I’m not sure it does!!! If the electrical analogy is correct, fuel should run from both tubes simultaneously at a flow rate inversely proportional to the line resistance. I suspect a hydraulic analogy would be more appropriate. Just saying😀😀😀

[Morala]

hi Sesman thanks for your input, will get the dictionary out to understand the lingo lol.I was wondering would it be possible to use a Y connector from the input lines going to the carbs and connect to the one outlet on the fuel tap thats working just a thought as not sure if the fuel feed would be enough to feed the carbs with only one fuel line working cheers.

[McCabe-Thiele (Ted)]

You need to keep both outlets, they will balance themselves out, I have fitted inline Aero filters to mine as well.

If you have worries about the other outlet blow up it, you might have something causing the pressure differential, I assume you have checked the filter, the tap internals etc.
If you connect the good flow side to one of the pair of carbs then turn on the tap the other side will undoubtedly flow with petrol.

[Bryanj]

Try it see what happens, 99.9% certain petrol will piss out of the unconnected spigot, as to the electrickery take two leads from a battery pos and connect one to the neg via a bulb then connect the other direct to the negvand see if the bulb stays lit! Always takes path of least resistance

[Sesman]

The petrol will flow in each pipe proportional to the resistance to flow path, not just in one path because the other has a higher flow resistance! There are other technical aspects to fluid flow that differentiate it from electricity: vacuum for example. I suspect that if each outlet flows independently you don’t have a problem. I’d connect both spigots and run the bike. If you suffer fuel starvation you will soon know!

[Sesman]

Try it see what happens, 99.9% certain petrol will piss out of the unconnected spigot, as to the electrickery take two leads from a battery pos and connect one to the neg via a bulb then connect the other direct to the negvand see if the bulb stays lit! Always takes path of least resistance

Nope. The resistance in each leg determines the proportional flow rate. Your ‘experiment’ simply confirms connectivity. Look up Norton, Thevenin and superposition theory.

[Sesman]

An example:

A 10V supply and two parallel conductors of 1 ohm and 2 ohms respectively.

The total current flowing will be approximately 15A with 10A flowing down the 1ohm leg and 5A down the 2ohm leg. Of course things get significantly more complicated when dealing with alternating currents and reactive components (capacitors and inductors). I am of course completely disregarding source impedance, which is the source current limiting factor.

Remove the 1ohm leg and 5 amps will flow in the 2ohm leg. Alternatively, remove the 2ohm leg and 10amps total will flow down the 1ohm leg.

What’s happened to the missing amps I hear you shout…😀😀

[McCabe-Thiele (Ted)]

When I studied fluid dynamics at Uni back in 1967-1971 the lecturer used the analogy of Pressure v Voltage, Flow rate v Current. It held up pretty well until we got to non laminar flow

[Sesman]

Absolutely,Ted. Our lecturers explained third order equations and reaction to input forces using the electrical properties of resistance, capacitance and inductance interchangeably with springs, dampers and fluid. It worked for a short while then things began to get more complicated 🫣.