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bad gas vs. fuel pump

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  • bad gas vs. fuel pump

    I'm a rookie boat owner. Boat purchased August of 2010 and fully serviced. The boat was owned by a good friend of mine who cared for the boat/engine in meticulous fashion. Boat powered by a 1988 Yamaha 200 v6 (only 253 hrs on the engine at the time of purchase). I do not know if the fuel pumps had been replaced at time of service last year or in it's recent past.

    Boat ran fine balance of 2010 and stored indoors over the winter (Bridgeport, CT). Ran fine first couple times out this year and then after a fuel refill (1/2 tank) began bogging down around 24 knots. Condition worsened to point where engine would stall after prolonged idle and/or 5 knots+-. I replaced fuel filter / separator unit, cleaned other fuel filter (the screened plastic insert), and sprayed carb cleaner into intakes. This did not resolve the problem. Noticed that the fuel primer bulb did not remain firm post engine stall - was able to restart by repriming. Other symptom was that at low speeds engine was notably vibrating.

    I'm wondering weather or not I just got some bad gas at the last fill up? Any means of further diagnosing before purchasing new fuel pumps? Is a flaccid fuel primer bulb post starting the engine always indicative of a fuel pump issue or does it depend on timing of when it goes limp (ok sorry starting to sound weird! ha!). In speaking with a service technician over the phone he seemed focused on the fact that the fuel primer had not remained firm post running the engine for a period of time and immediately deferred to the fuel pumps as being the likely culprit. Makes sense to me but again the timing of the problems only appearing after that one fill up of gas has me wondering. Should I run the engine dry and re-fill, check it out ahead of replacing pumps?

    Anyway any ideas welcome. Thx.

  • #2
    once the engine is running as both the fuel filter cup on the engine AND the fuel primer bulb are on the suction side, both will run about half full.
    the bulb will NEVER EVER stay firm when running or after engine shutdown on a normal running engine.
    however a bulb that wont pump up firm in a few squeezes can indicate leaks in the system or a ruptured pump diaphram.
    find a tech that understands how the primer system works.

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    • #3
      You can do a simple check to see if it is the fuel pumps, start with the top fuel pump and loosen the 2 10mm bolts that hold it on (but do not remove completely) pull the fuel pump away a bit and pump the primer bulb. If the fuel pump is bad it will leak fuel out of the back of it. If not tighten it back up and try the others. If all are good its prob your gas, prime the system with the bulb again and check for leaks before starting. Have a rag handy

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