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2003 90HP - Engine suddenly runs rough & stalls

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  • 2003 90HP - Engine suddenly runs rough & stalls

    On my way back to the boat ramp this past Friday (Tampa/Little Cochroach Bay), I slowed down to idle to secure some loose gear. As I attempted to get back underway, my 90HP engine (Mod #90TLRB) started running very rough and sputtering and the boat (17ft Sea Pro) would not get on plane when normally it jumps right out of the water. After verifying I hadn't picked up something in the prop and the engine wasn't overheating, I revved it in neutral but it still missed and sputtered. Luckily I was only a couple of miles out and was able to "limp" back to the boat ramp at about 1/4 normal cruise speed with the engine sounding rough. As I approached the ramp at idle speed, the engine sputtered/sneezed and conked out a few times but I was able to safely dock and load it on the trailer.

    The next day I pulled the spark plugs and they all looked good with no carbon buildup or discoloration. I then pulled the fuel filter/water separater and dumped the fuel in clear plastic container. There was no sign of any water or other contaminates in the fuel. I also installed a new fuel/water separator.

    I then pulled and disassembled each carburator thoroughly cleaning using decarb spray and compressed air. The only item I could not disassemble were the brass hexagon shaped "Valve Seats" located to the right of the Main jet/nozzle and Pilot jet (see attached pics). After reassembly and putting the carbs back on, setting the idle screws open at 1-1/2 turns, and verifying no fuel leaks after squeezing primer ball, I started the engine. Unfortunately, it still runs rough and stalls.

    Note this was the first time I had the boat out after about 3 months. But I always start and run the engine at idle (with water hose connected) at least every other week when not regularly used. I also treat the gas with Startron to neutralize ethanol issues. That morning I added about 17 gallons of new premium fuel to top off the 30 gallon fuel tank. Given these facts, I don't think the problem is fuel contamination or a carb issue.

    Could the fuel pump be bad and is there a way to test it? Any other ideas as to what might be causing this problem?

    Thanks!
    Attached Files
    Last edited by CaptBrian33; 03-18-2013, 03:06 PM. Reason: spelling

  • #2
    Have you thought about checking compression, spark, and timing to start out with?
    If all that is good then check fuel pump

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    • #3
      I normally would and probably should have checked compression, but since the spark plugs all looked clean I didn't bother. Because I am not familiar with how to check the timing or spark, I've gone ahead and brought it to an authorized Yamaha mechanic to be serviced. I am still hoping it's only a bad fuel pump and nothing more serious. Should know in a day or so...

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      • #4
        Mechanic says Carb Pilot Screws just needed adjusting and I had set them to run a little too lean (hadn't opened the full 1-1/2 turns after cleaning - DUH!). 1 hour labor including running it on the water and he says its good to go. He also said the original loss of power and sputtering was likely due to the carbs needing cleaning. Seems to be idling ok now - not real smooth but isn't that normal with 90hp 3 cylinder Yams?? Hope to get out on water tomorrow and test for myself...

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        • #5
          Good to hear it is up and running well again.
          Your 1st post said you set pilot screws to 1 1/2 turns out, so I am puzzled that is all he had to do to make it run OK

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