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Thread: Oil pump....Fuel pump problem?

  1. #1
    Junior Member Mini
    Join Date
    Jan 2020
    Location
    Lebanon, ME
    Posts
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    Default Oil pump....Fuel pump problem?

    I have a 1999 vmax 500 ERC. Engine fried and I have completely rebuilt it. When taking the engine out of the sled I noticed the oil line coming from the oil pump to the fuel pump was full of gas and not oil. After rebuilding the motor and reinstalling everything, I bled the incoming oil line to the oil pump and the pump itself. When I pulled the out going line off the oil pump to bleed it, it was full of gas again. After putting a 50-1 mix of oil in the gas tank to protect the engine, I started it and pulled the oil line off the fuel pump. I had a steady stream of gas out of the fuel pump and no oil from the oil pump. I had a second oil pump and swapped them out and ended up with the same problem. The engine runs great so the fuel pump is working but not sure why the stream of gas is coming out of the fuel pump when I pull the oil line. Is this normal or is part of the fuel pump not working? I don't believe I have 2 bad oil pumps? What am I missing? Thanks in advance!!!!

  2. #2


    Default

    Is there a check valve in that line that goes from the oil pump to fuel pump ?
    If so, there is an arrow on it, make sure it is pointed at the fuel pump, not oil pump.
    -------------------------
    1997 Yamaha XTC
    700 Redhead, Mr. Viper ported, CPR pipes, SRX reeds, Heelclickers, Dual bulb, LT Ohlins

    1997 700 SX
    Thinned head gasket, Gutted Airbox, Reed Spacers, Bender Pipes, Viper Shocks, 51/43 helix 89L weights

    2004 Viper S
    SLP pipes, peak performance head,

    2001 SRX 700
    Power Inc. Pipes, Loaded 8DN20's, Hauck Y 51/45

    1997 Mountain Max 700
    Black XTC Hood, Thinned Head Gasket, Gutted Air Box, Reed Stopper Notch, SLP Pipes

  3. #3
    Junior Member Mini
    Join Date
    Jan 2020
    Location
    Lebanon, ME
    Posts
    4


    Default

    There is no check valve. Is there supposed to be one? There wasn't one on it originally.

  4. #4


    Default

    Nope, sorry, that's just for triples.
    Could have the crankcase hose and oil pump hose got switched at the fuel pump by chance ?
    -------------------------
    1997 Yamaha XTC
    700 Redhead, Mr. Viper ported, CPR pipes, SRX reeds, Heelclickers, Dual bulb, LT Ohlins

    1997 700 SX
    Thinned head gasket, Gutted Airbox, Reed Spacers, Bender Pipes, Viper Shocks, 51/43 helix 89L weights

    2004 Viper S
    SLP pipes, peak performance head,

    2001 SRX 700
    Power Inc. Pipes, Loaded 8DN20's, Hauck Y 51/45

    1997 Mountain Max 700
    Black XTC Hood, Thinned Head Gasket, Gutted Air Box, Reed Stopper Notch, SLP Pipes

  5. #5


    Default

    Since you have some oil in the gas already, try pulling the line off the fuel pump that comes from the oil pump.
    Plug fuel pump with something so fuel doesn't pour out. I used a small piece of hose with a golf tee stuck in it.
    Then start the sled and hold oil pump wide open, see if you get oil coming out of the line. If so, your good to go.
    Had to do this with a Viper recently.
    -------------------------
    1997 Yamaha XTC
    700 Redhead, Mr. Viper ported, CPR pipes, SRX reeds, Heelclickers, Dual bulb, LT Ohlins

    1997 700 SX
    Thinned head gasket, Gutted Airbox, Reed Spacers, Bender Pipes, Viper Shocks, 51/43 helix 89L weights

    2004 Viper S
    SLP pipes, peak performance head,

    2001 SRX 700
    Power Inc. Pipes, Loaded 8DN20's, Hauck Y 51/45

    1997 Mountain Max 700
    Black XTC Hood, Thinned Head Gasket, Gutted Air Box, Reed Stopper Notch, SLP Pipes

  6. #6
    Junior Member Mini
    Join Date
    Jan 2020
    Location
    Lebanon, ME
    Posts
    4


    Default

    Ill try that. Thanks!

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