carb vs fuel delivery? question

Discussion in 'Outboard Maintenance' started by KeepingItSimple, Mar 20, 2011.

  1. KeepingItSimple

    KeepingItSimple Well-Known Member

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    Hey guys, new to the forum. Just bought a pathfinder 17t and digging it so far. Perhaps you can help me out with a prob that seems to have surfaced. This is a little convoluted but I'll try and keep it simple.

    60hp Yamaha. Precision blend/2-stroke.

    Last week right when I got to the ramp it acted a little fuel starved. You know, that sort of higher pitched higher rev sound like it's fixin to run out of gas. If I kept it in gear and gave a little throttle it would stay running. If I got near idle it would die. The fuel line has one of those cheap inline fuel filters with the glass cylinder right before the fitting to the motor. Watching it while running, to me it looks like there is very little gas making it through - just a slow trickle - and the cylinder keeps a lot of air in it. So (and I know what you're thinking), I ran it on a new line off a portable tank. Even had an extra one of those glass filters that I put inline to compare. Again, it looked like it just wasn't pulling fuel with little fuel being pumped through. So I'm thinking fuel pump. I take it apart - looks fine (which I know isn't 100% confirmatory). I'll replace the plastic and rubber gaskets as that's simple enough. The odd thing is that it runs reasonably well at wot. Also, I can't get it to keep running at idle when I keep that glass thing filled by pumping the bulb.
    What gives?

    Thanks for the opinions.
    Alex V
     
  2. Brett

    Brett > PRO STAFF <

    There is a simple way to pressure test an outboard fuel pump.
    One I learned from a shade tree mechanic years ago.
    After activating the kill switch and removing the spark plugs so the engine couldn't start,
    he'd remove the short fuel line from the fuel pump to the carburetor,
    and replace with a longer hose. This would allow him to extend the end of the hose
    from the output side of the pump into a wide mouth container.
    With a second person assisting, he'd place his thumb over the end
    of the hose from the pump, then using the fuel line primer bulb,
    fill the fuel system with fuel all the way to his thumb.
    This removed all the air out of the pump and fuel lines.
    Then, with his thumb held tightly over the end of the hose,
    the assistant would pull the starter cord a few times
    letting pressure build up in the fuel line, held in check by his thumb.
    Aiming the hose into the container, he'd let his thumb lift
    slightly from the end of the hose, directing a jet of pressurized fuel
    into the container. If there was no jet of fuel, a second attempt would be made.
    If still no stream of fuel squirted past his thumb, then the pump needed rebuilding.
     

  3. KeepingItSimple

    KeepingItSimple Well-Known Member

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    From what I see going through the glass cylinder fuel filter and from watching how slowly the fuel drains out of the other plastic filter on the side of the motor just before the pump, my suspicion that there's a high pressure stream is nil. I think I'm gonna spend the $35 for the rubber parts to rebuild the fuel pump.
    Thank you.
    Alex V
     
  4. iMacattack

    iMacattack busy, too busy

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    Also look at the anti siphon valve at the fuel tank. This was a common problem (I had to replace mine on the 17T I owned). I thought I was having a fuel problem and it turned out to be the anti siphon valve.

    http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1247153549/31
     
  5. KeepingItSimple

    KeepingItSimple Well-Known Member

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    If it is the antisiphon valve, would I still be able to pump fuel through easily with the ball? Thank you.

    Alex V
     
  6. cutrunner

    cutrunner Cert. Yamaha technician

    Another way to check the fuel pump on your motor is to unbolt it from the side of the motor with the two ten millimeter bolts that hold it on, squeeze the primer bulb, if no fuel shoots out of the diaphram , its good. If fuel shoots out replace it.
     
  7. KeepingItSimple

    KeepingItSimple Well-Known Member

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    Someone on another forum suggested that it's the idling jets/passage ways. Thoughts?

    Thank you.
    Alex V
     
  8. Brett

    Brett > PRO STAFF <

    It's a fuel "system", any part can affect how the engine runs.
    From your description so far, it sounds like an air leak,
    somewhere between the fuel pick up and the carb.
    If you don't find an air leak and the fuel pump is ok,
    then you get to look at the carb, linkages and ignition system.

    Sounds like fun to me.... ;)

    How old is the boat and outboard? :-?
     
  9. iMacattack

    iMacattack busy, too busy

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    Yes you would. Bonus point is that changing the anti-siphon valve is cheep, about $10 or less and easy.

    If it has not been done it might be worth a look.
     
  10. KeepingItSimple

    KeepingItSimple Well-Known Member

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    Fair enough. I'll change the fp guts and do the antisiphon thing. It's a 2001. Due for some maintenance I suppose. Those things are pretty easy. Totally rebuilding the carbs is a bit more work - I think I'll hold on that for now. Shoot, just taking the carbs completely off is no joke with the oil tank and all those tubes and the couple of linkage points.

    Alex V.
     
  11. Brett

    Brett > PRO STAFF <

    10 years old, yeah, it's time for a fuel system rebuild.
    That was a pre-E10 fuel system and engine.
    No telling what you'll find when you start checking closely.
    If/when you replace parts, make sure they're ethanol compatible.