Using vent hose from fuel tank

I have an 03 r1200cl with a Hannigan sidecar. I replaced the right saddlebag with a 3gal. Rotopax. I used the tank vent that used to go to the charcoal canister to connect the Rotopax to the fuel tank. It seems to work fine the vacuum from the tank pulls the fuel from the cell into the tank as it is being used. After the bike is shut off you can hear fuel trickling into the tank as there is still vacuum present. This leads me to believe that the bike is using fuel faster than it is being transfered. The Rotopax is vented to atmosphere. Does anyone know if pulling full from the back of the bike will put extra strain on the fuel pump and cause problems with it in the long run. Thank you in advance.

The tank vent has a built-in rollover valve, the orifice of which was sized to flow the right amount of AIR to keep the tank from building vacuum. That means that the orifice is too small to flow the same cc/min of FUEL. So, vacuum build is the result. How much it builds depends on your rate of fuel use and time. It is possible if you run fast enough and long enough that you will implode the tank. Most likely starving the bike for fuel or imploding the tank will happen before you damage the fuel pump. When I converted my R1150 and R1200's to vent fill from a permanently mounted auxiliary tank, I removed the rollover valve from the tank and replaced it with one in the aux. tank. After that the main tank did not build vacuum and when the aux. tank was empty, the main tank vented through it. I would only use this solution for a permanently mounted auxiliary tank - not a portable or temporary one.

You say that the Rotopax is vented to atmosphere, does it have a rollover vent? If not, you might have created a potential danger in a crash or upset situation.

Here are some pics from the R1200 FYI...

This shows the rollover valve on the R12GS



You can see on disassembly that the vent orifice is small. Maybe it could be enlarged while still keeping the valve, but I did not try. That would be one way to reduce the vacuum level in the tank and speed up the fluid flow.



With the valve removed the fill neck was reinstalled. The thin vent hose was replaced with fuel injection hose...



Finished installation of aux. tank. It has two (redundant) NHRA approved rollover vent valves in it.



Before the permanent auxiliary tank I used a RotoPax, but I would not have attempted to plumb it inline...

Do all BMW bikes have that vent check valve?

This is the Oilheads forum. This post needs moving to the Camheads/Hexheads forum where you can get answers from 1200 owners.

happy wanderer said:

This is the Oilheads forum. This post needs moving to the Camheads/Hexheads forum where you can get answers from 1200 owners.

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The Op has a R1200CL. I think that model is a Oilhead.

Lee said:

The Op has a R1200CL. I think that model is a Oilhead.

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Oooops. Saw the 1200 and photos of a 1200 and assumed it was a 1200. My bad! Yeah the cruisers are oilheads though!