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Yamaha 50hp 4 stroke carb problems

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  • Yamaha 50hp 4 stroke carb problems

    Bought a second hand 1995 Yamaha 50hp four stoke. Test run on bench seemed OK. Left sitting with dry carbies for 3 months then installed on boat. One carby flooding so stripped and cleaned all carbies - no improvement.
    Bought 4 carby kits, stripped and soaked carbs in truckwash. Cleaned and installed kits. Noticed some pitting in carb bodies. Now 2 carbs not working at all (no draw on vac gauge - needle bouncing) and 2 carbs showing steady vac on gauge. Have stripped and checked a couple of times since but can't pinpoint problem....
    Any ideas or am I up for a new set of carbs?

  • #2
    I would start with a leak down test to make sure cylinders are sealing properly if 2 are not pulling a vacuum.

    Did you follow your manuals procedure for link and sync after reinstalling carbs on motor? needs to be done every time to make sure carbs are open exactly the same


    • #3
      Thanks for that.
      I checked valve clearances and did a compression test first up but don't think I have internal problems as the motor ran smooth when I first got it and ran it for a few minutes.
      I don't have a manual but intended to sync carbs using vac gauge for initial set up then fine tune using home made manometer.
      With motor set at fast idle and carb linkages disconnected it is possible to rev motor by opening individual throttle link on working carbs but motor stalls if I open throttle on 'dud' carbs....