Getting fuel from bottom of a frisco sporty tank???

[farmall]

I run the siphon method in my xr650r. Low side of the tank is the non petcock side, so I run a hose over the tunnel to the other side. Never had it fail to function, but if I did I could turn it to reserve and use fuel from the petcock side(as the intended purpose is when that side goes empty).

That siphon design maintains siphon because the tube is not open to atmosphere and the fuel on one side of the tank has plenty of surface area for atmospheric pressure.

[ChopperDani]

That siphon design maintains siphon because the tube is not open to atmosphere and the fuel on one side of the tank has plenty of surface area for atmospheric pressure.

So what you are saying is, if you chose to do this siphon design, run the line to opposite side of the petcock and it will work versus if the line was on the same side as the petcock?

Im, really interested in this topic. I might try this siphon deal until I can come across a shitty used peanut tank i can true frisco.

[Dougtheinternetannoyance123]

So what you are saying is, if you chose to do this siphon design, run the line to opposite side of the petcock and it will work versus if the line was on the same side as the petcock?

Im, really interested in this topic. I might try this siphon deal until I can come across a shitty used peanut tank i can true frisco.

If you had a fuel pump (EFI model bikes) you could probably pull off a siphon idea, but in the real world siphon feeds dont work in my experience/opinion. I have several bikes that have feed issues and work fine when the tanks are over 1/2 full but never run low as they cut out and stall. I have cleaned, replace petcocks, re-routed hoses and everything under the sun. HDs and vintage British vibrate like crazy and the fuel inside sloshes around so any surface tension, atmospheric pressures or other issues are theoretical, not practical.

If you have a tank with paint you dont want to disturb, find a talented welder and purge the inside with inert shielding gas, use a well set up tig, copper plate (Copper plate backup/diffuser is even better) and carefully weld in a new bung location with minimal heat and distortion. At a former job in a Aerospace plant we used weld chambers with totally Oxygen free welding environment. (Big box with a pump, sealed doors and glass window.. You stick your arms thru inside thick rubber gloves and tape your weld shield to the glass.) I used to take in a LOT of motorcycle parts to work and repaired a lot of parts this way. You CAN make a weld chamber or,, a backyard box that mimics this. You can weld paper thin metals this way or almost no heat except at the point of welding.

Lacking that, you COULD try and fab up a sandwich no weld setup , I have seen some industrial methods for this, but cant think of where you could order them. Its basically 2 machined small plates with Nitrile O rings and a threaded ID/OD center post. You tighten down the OD gland nut and it sandwiches them together sealed, The ID is threaded for your pipe fitting (Petcock). On farms and industrial apps you use this to add a pipe fitting to a plastic drum or vessel, but I have seen a few setups on metal where welding was not feasible. On a motorcycle tank, it COULD be done but I would think would eventually leak.

Many asian bikes use a similar setup with well nuts and a large casting petcock with a O ring because the metal on those tanks is so thin.

Some of the local club bikes use a certain frisco style on their builds, especially the Outsiders MC, You take a sporty peanut tank, remove the bottom/tunnel, weld in a flat base with room for mounts. Cut off the filler neck and add a smoke stack style extension and it projects up above the tank so its higher than the rest of the tank. Add a petcock to the rear most part of the tank, often at a angle so the pickup projects in and room.
I have a few pix of some of their bikes, Years back, a lot of the club bikes were swedish style with frisco tanks.
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Funny story, One of my favorite gear heads was Smokey Yunick, Anything he did or wrote is worth studying. In his years in NASCAR he would never purposely cheat, It was what was NOT in the rule books that was the key and lots of stories about the tricks he pulled. At that time there was a rule about the SIZE of the fuel tanks, not how many or what type of tanks. So, not real safe, but he ran fuel INSIDE the frames and roll cages. The other racers and the track KNEW something was up as its a huge advantage to not have to pit for fuel as often. Doing the math no way could his car do that many laps and not stop for fuel.
After their car won the race at Tech inspection they tore the car down and had the tank out but could not figure it out. He knew eventually they would figure it out but got tired of waiting for hours on end, so walked over and despite the fuel tank sitting on a work bench, jumped in the race car and fired it up and drove it back to their pits.
So, Point of the story is, if you LIKE your tank and the style but want more capacity, you CAN add capacity in another location. (Tool bag, inside frame tubes, under the seat. Crazy sissybar-fuel tank,, its all been done)

[farmall]

So what you are saying is, if you chose to do this siphon design, run the line to opposite side of the petcock and it will work versus if the line was on the same side as the petcock?

Im, really interested in this topic. I might try this siphon deal until I can come across a shitty used peanut tank i can true frisco.

He said it works. I said the theory is sound. (Pipe diameter may affect performance.) When the tank is filled (above the division between both sides) the siphon is filled and of course not siphoning until there's a level disparity to make that happen, so every fill the siphon is primed though there might be a small air pocket. With both ends of the tube immersed in fuel when one side goes low it's reasonable the other would siphon.

You could test by making a copy of whatever you want to use to test outside the tank since only the relative liquid levels matter.

https://www.youtube.com/watch?v=awq-XP5bV18

To test just the principle without cutting metal, instead of suction etc. (as in video) you could immerse a straw in a container to fill it, then place one end of the straw in a container of water whose liquid level is the same height. Now you have a static system full of water. Take another straw and without disrupting anything suck water out of one container and observe flow from the other.

Check https://www.youtube.com/watch?v=4IVc7oq29Uw and many more...

If it was mine I'd still make sure and cut and weld the tank/a tank.

DTIA wrote:
If you have a tank with paint you dont want to disturb, find a talented welder and purge the inside with inert shielding gas, use a well set up tig, copper plate (Copper plate backup/diffuser is even better) and carefully weld in a new bung location with minimal heat and distortion. At a former job in a Aerospace plant we used weld chambers with totally Oxygen free welding environment. (Big box with a pump, sealed doors and glass window.. You stick your arms thru inside thick rubber gloves and tape your weld shield to the glass.) I used to take in a LOT of motorcycle parts to work and repaired a lot of parts this way. You CAN make a weld chamber or,, a backyard box that mimics this. You can weld paper thin metals this way or almost no heat except at the point of welding.

Nothing like an official purge chamber! (Didn't BSA use those for their titanium-framed race B50s or similar?) You could seal off a cheap blast cabinet with duct tape as an expedient but argon ain't cheap.

He could back purge conventionally by sealing the cap and connecting the purge regulator to the fuel valve hose barb after THOROUGHLY removing old fuel with an aggressive detergent.

[Guest]

For whatever reason someone’s siphon doesn’t work, I highly doubt it’s due to some minor fuel sloshing around and vibration of a road bike.

My xr spends plenty of time one wheel on the ground, no wheel on the ground, bars on the ground, me on the ground, still gets fuel....

From my petcock I run up about 4” over the tunnel and down about 7” on the other side.