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  1. #1

    Primer bulb functioning half?

    Hello everyone,

    I'm at a bit of a loss with our two Optimax 90 (1B802995 - 1B803159) and their primer bulbs.

    If the engine sits for a while, say 10 minutes or so, I cannot pump fuel through the fuel line with the manual primer bulbs. The fuel simply doesnt get sucked upwards through the line. The odd thing is, if I disconnect the line at some stage after the bulb (Either at the engine or directly at the bulb) and pump a little bit, fuel gets sucked up. When I close it then, I can pump the bulb until its hard. I do point the arrow upwards, skywards, when I try to prime.

    I have so far tried:

    1. Used another fuel tank to make sure the pickup is not the problem.
    2. Used another brand new pump. The old pumps work perfectly as well and have no more than 10 hours of use on them.
    3. Used new fuel line to make sure there is no problem with the existing one.
    4. Double checked the vent on the existing fuel tanks, they both let air in.

    The problem occurred suddenly and at both engines at the same time, even though they are both completely separated from each other - own fuel tank, etc. I found that I can also temporarily fix the problem when I pump while I crank the engine. For whatever reason this allows me to again pump a bit of fuel into the primer bulb and once a bit of fuel is in there I can pump it hard.

    I have recently overhauled the engines and taken literally everything apart, cleaned it and put it back together. The engines ran great for the first 10 hours or so and once I'm able to pump fuel to them they will run happy for hours, no matter the RPM.

    I somehow doubt that the problem is at the engine side, but since I have changed everything else already (Fuel tank, fuel line and primer bulb) I'm a bit at a loss.

    Thanks in advance for any input.

  2. Member
    Join Date
    Jun 2013
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    #2
    are these fuel lines and engines sitting in direct sun and heat when this happens , in extreme heat 100 plus
    .................................................. ...the scariest thing in life is the unknown ...................................

  3. #3
    Hey Joe,

    yes about half a meter of the line sits in sunlight. From the tank to the bulb its in the shade. I had these lines routed this way for the last 10 years without any issues - The lines are not 10 years old, I'm just talking about the setup.

    Just to make sure there are no vapor issues I went back to the boat well after sunset when everything cooled down and its still the same.

    What bugs me is the moment I disconnect the line either at the engine or directly after the primer bulb I can pump it right up. It made me think about a bad vent in the VST or something similar, but I had it open and it worked absolutely perfect.

    Just a thought - What should I expect when I blow into the fuel line? Am I correct in assuming it should go right through and out of the vent hose of the VST? While I have checked the VST, I have not checked the hose that vents the vapor down towards the middle unit. Could this be plugged and cause the issues that I see?
    Last edited by One Ocean; 08-20-2019 at 11:40 PM.

  4. Member
    Join Date
    Jun 2013
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    LONGVIEW TEXAS
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    #4
    if inlet needle is closed cant force air through it,check vent hose for kinks and plugged
    .................................................. ...the scariest thing in life is the unknown ...................................

  5. #5
    Checked everything and I can blow air through the primer bulb right out of the vent hose of the VST.

    This morning the problem disappeared on one of them magically. I will tear everything from the VST down to the primer bulb apart. There must be something that I miss.

  6. Member
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    Jun 2013
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    LONGVIEW TEXAS
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    #6
    gota be
    .................................................. ...the scariest thing in life is the unknown ...................................

  7. Member lpugh's Avatar
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    May 2009
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    Sacramento Ca
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    5,164
    #7
    Does it start when this occurs? If it does this would suggest the vst may be full and valve closed which is what I suspect
    If the needle valve is closed such as when the vst if full there is no way for the vapors in the bulb and lines to bleed thus the bulb will not get hard, can not compress liquid but vapors will easily, thus soft bulb
    Make sure there is no unneeded fuel line, try to run it uphill with out any low points where vapors may get trapped. Mount the bulb with the arrow pointed upward all the time, this greatly adds in purging vapor bubbles. Try to keep the lines out of sunlight as much as possible and use a high quality top brand top tier fuel that may have lower Reid Vapor pressures

    You have experienced what is known as vapor lock, todays fuels are designed to be under pressure not a vacuum condition and high temps
    Modern fuel has a starting boiling point of a about 90 degrees for the light ends and goes up from there. The point being, at 100 degrees you will have vapors in the lines, the trick is getting them to purge easily

    With all that said the last time I pumped the bulb up on my motor was when I installed it about a year ago though my boat rarely goes unused for two weeks
    Please do take note though that if the fuel has evaporated out of the vst that the fuel pumps will be running dry which really is not a good way of treating them. I have never had a electric pump failure on any outboard yet. Not arguing Mercurys recommended procedure, just stating my experiance

    Last edited by lpugh; 08-29-2019 at 09:34 PM.
    Thank You Leon Pugh