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1997 200 HP Yamaha lean sneeze issue

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  • 1997 200 HP Yamaha lean sneeze issue

    Model is - S200txrv
    I have a new to me engine that I believe sat for a couple of years. I have the engine running but it seems to have a lean sneeze on slow acceleration. If I put it to WOT immediately it does not have this issue. It just occurs during slow acceleration.
    I have changed the fuel pumps, spark plugs, fuel filters, primer bulb and rebuilt the carbs multiple times. When cleaning the carbs I put them in carb cleaner for a few hours then put in an ultrasonic cleaner. I also cleaned the jets. The timing looks good as do the plug wires. Compression is also good.
    The issue still occurs even when I prime the bulb during acceleration. It idles fine and at WOT it runs good.
    At this point I am not sure what the issue could be. The one area that may be a problem could the oil ratio? Since the oil system is so old, I have been premixing the gas at 50 to 1 in addition to the oiler (which also seems to be working.) Is it possible the heavy oil mix is causing a slight lean condition in the mid-range rpm on acceleration? Any other ideas on what could potentially cause the issue?
    Thanks for the help!

  • #2
    Just my thoughts, but mixing oil in the tank could change the SG of the fuel going thru the jets/passages making it not how they designed the system


    • #3
      Thanks - I am going to try running in an external tank without premixed fuel and see if the condition goes away.


      • #4
        Have you check timing marks and initial carburetor screw adjustment? lean sneeze and pre-mix are different issues, unless your cylinders scorned so much that piston drugging in cylinder, that usually started with lean sneeze. my recommendation: remove heads, inspect cylinders, clean water passages that most likely long overdue anyway. and adjust according to service manual. all my 2-cycle engines start and run perfect: outboard, lawn mover, power washer, power saw. all never required adjustments once set properly and drained of gas before winter storage.


        • #5
          Yes I have adjusted the initial carb mixture screws as well as set the timing. I will definitely look to remove the heads if I continue to have the issue. Thanks