Replacing the in-tank fuel pump with an external one

Discussion in 'GS Boxers' started by space, Feb 8, 2014.

  1. space

    space a.k.a. Jake

    Joined:
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    I made this modification to my HP2 Enduro, but it would likely work for any of the oil/hex/wet heads. Certainly for the hexheads, at least. That said, this will not improve the performance of your bike or reclaim more than a liter or so in the stock tank. But if you like to muck about in the garage and/or void warranties, read on!

    I first considered this mod because I have an aftermarket HPN tank on my HP2, and I found that the intake sock of the stock pump didn't reach to the bottom. At one point this left me stranded in the New Mexico desert, despite there being a few liters still in my tank. When my fuel pump spontaneously died one day, I took it as a sign that it was time to replace it with something better.

    Here's an overview picture of what I did. I'll give the ingredients (manufacturers and part numbers) at the end of this post.

    [​IMG]

    First, notice the hoses in braided metal. Those are 8 mm (5/16") ID hoses that connect to the taps on the three lobes of the HPN tank. If I did this again, I would use hose with a abrasion-resistant fabric jacket rather than metal, as any unfinished metal ends are nasty little bundles of hypodermic needles. Fun!

    I replaced the HPN petcocks with my own design, which allows me to use quick disconnects:

    [​IMG]

    Because they drain from the very bottom of the tank, they can run it dry, with no worries about gas left below the intake sock. In the event that you are interested in doing this mod on an HP2 with an HPN tank, I had a lot of these machined -- 30 was not much more expensive than 3 -- and I'd be happy to sell them at cost.

    [​IMG]

    The metal lines connect the three taps of the tank to a pre-pump fuel filter, with a 100 micron screen. The pre-pump filter is the cylinder immediately in front of the alternator. Fuel then routes into a solenoid that selects between the main tank and an underseat tank (the Bavarian Markus tank, for the HP2E/SM only). It could also easily tap into any other aux tank, or simply be replaced with a 90 degree bend to go straight into the pump.

    Looking back at that first pic, you can see that the fuel pump is mounted on a home-made carbon fiber piece with vibration-isolating rubberized clamps. After the pump, fuel flows through a 90 degree bend, and a 10 mm filter (the ribbed silver cylinder) before being sent to the pressure regulator and the injectors.

    [​IMG]

    This side view shows how the hoses are routed with the tank in place. Some care must be taken with the length of the hoses to avoid them getting pinched. The fuel pump is powered by the stock pump controller. I cut off the blue connector that normally goes to the pump (blue and yellow wires, if I recall correctly) and spliced in my own connector, which goes to my pump. Shockingly this works without any error codes. You can see in the above pic how the pump controller is mounted to the rubber spacers for the tank.

    Excess fuel returns to the main tank in the normal way:

    [​IMG]

    Note that the tank no longer has the fuel sender line or the electrical connections to run the in-tank pump or measure fuel level. I found the stock fuel float to be pretty worthless with the HPN tank, so I removed it. I feel reasonably safe doing this because I have the aux tank as backup. Incidentally, you can also see that the vent line runs backward rather than forward on my bike, which makes room for a steering damper.

    Inside the tank, I removed the stock fuel pump, float, and filter to make a bit more volume for fuel. The stock filter is glued in place (inside that white plastic housing) and removable with a dremel or similar implement of destruction. I principle I suppose it's nice that I can now clean or change my fuel filter, but in practice I've never heard of a hexhead filter fail. (And I've read JVB say the same thing, so that's good enough for me.)

    The last component is the connection to the aux tank. That routes through another 100 micron fuel filter to protect the solenoid and pump:

    [​IMG]

    This setup avoids needing a secondary pump to transfer gas from the aux tank to the main. The main fuel pump is very quick, fully transferring the 7 L held by the Markus tank into the main tank (less whatever fuel is consumed) in about 3 minutes.

    I have two items on my to-do list. First, I'd like to add a second solenoid on the return line so that I can transfer fuel from the main tank to the aux tank. That way I never need to remove my seat and fill the Markus tank directly. Second, I'd like to add a fuel level sensor for the main tank. If I ever get around to this, it will almost certainly be a DIY bubbler system.

    Here are the parts that I used:

    Pump: Walbro GSL393
    Purchased from fuel-pumps.net, which also provides the mounting clamps and pipe fittings.
    Pump is rated at 155 L/hr, which is a bit more than the stock pump's 110 L/hr. That won't buy you any additional performance, as the extra fuel is sent back by the pressure regulator. Current draw is comparable to the stock pump.

    Solenoid for selecting the aux tank: Greasecar SV100 valve
    Mainly chosen because it has the right size/port configuration to fit my needs. Also seems to have a solid track record with the waste vege oil / diesel conversion community.

    10 micron fuel filter: Golan mini reusable filter
    Nice piece of kit. The metal filter element can be popped out and rinsed in the sink to clean it. Lots of KTM'ers use these as replacements for the stock filter.

    The 100 micron filters and the rest of the plumbing are from Russell, mostly purchased on Summit Racing.

    All in all, I'm very happy with this mod. I've put over 5000 miles on it without problem. Like I said at the start of my post, I wouldn't recommend this if you don't have a good reason for doing it, but perhaps it will be useful to someone else with a dead pump and an urge to tinker.
    #1
  2. mini151

    mini151 Adventurer

    Joined:
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    SLC, UT
    Very nice job.
    #2
  3. Yearroundrider

    Yearroundrider Tim.

    Joined:
    Nov 16, 2011
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    438
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    Hollister Ca
    Random question, do you have over heating problems?
    #3
  4. space

    space a.k.a. Jake

    Joined:
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    No overheating problems. The external pumps are designed to be cooled by fuel flowing through them rather than by being in a fuel bath.

    EDIT: come to think of it, that must be true of the internal pumps as well, because they're no longer submerged when the tank is half empty.
    #4
  5. _cy_

    _cy_ Long timer

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    Nice job!!!!
    #5
  6. Parkinoff

    Parkinoff n00b

    Joined:
    Jul 16, 2008
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    Location:
    Western Cape South Africa
    Hi Jake, you mention that you've made a few extra HPN tank fuel outlet fittings: "Because they drain from the very bottom of the tank, they can run it dry, with no worries about gas left below the intake sock. In the event that you are interested in doing this mod on an HP2 with an HPN tank, I had a lot of these machined -- 30 was not much more expensive than 3 -- and I'd be happy to sell them at cost." I would be interested in buying two of these fittings if you still have some for sale. Regards, Peter
    #6
  7. space

    space a.k.a. Jake

    Joined:
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    Yes, I still have some fittings available. PM coming your way ....
    #7
    leolou likes this.