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  1. #1

    Low Fuel Pressure ??

    Good Morning All,

    Was wondering if there is a fairly easy way to “Bench Test” my new Mikuni Triple Out fuel pump and also how to test my vacuum pulse line from the engine block. The reason I ask all this is because the fuel pressure seems very weak to me. Left un-assisted, the pump will not pull fuel all the way from the tank on it’s own. I have to prime the carbs manually. Once it’s running, I can see into my clear plastic fuel filter and it takes a while to build enough fuel not to “bogg” on acceleration. Initially when I first installed the pump, I thought I could see a very good flow of fuel coming into the filter. Unfortunately I also found a cracked cylinder at that time. I have since replaced it, but now the fuel just dribbles into the filter.
    Once it is all primed up and past the “bogging”, it runs GREAT. Until I shut it down for a few minutes to smoke a cigarette or so. Then, it will start on it’s own, but will bogg down on acceleration again for a while until it will eventually run full throttle once again.
    The pump is brand new and I have new lines everywhere, including a new pulse hose shorter than the 12” mentioned. I have bypassed the fuel on-off-reserve valve straight from the reserve line to the pump, and have the fuel cap removed, for testing purposes. I can blow backwards thru the line into the tank effortlessly.
    Any and all suggestions are welcomed and appreciated.

    Thanks in advance,

    Jeff Galloway

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    You can put a vacuum pump on the fuel pump pulse fitting and apply say 5 in. It should hold indefinatetly. (testing the diaphragm seal)

    Pulse hose, just make sure it's clear and hose clamp is tight. (short as possible for strong signal)

    Make sure your tank vents are routed correctly. The fuel pump shouldn't have to "pull" the fuel from the tank all the way. Slight pressure (1 psi) should be inside the fuel tank helping to "push" the fuel to the pump.

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