Yamaha 150

Discussion in 'Bubba's Outboards' started by srjones, Jul 15, 2007.

  1. srjones

    srjones New Member

    Messages:
    18
    State:
    midwest city, ok
    I've got a question about my father in laws motor. It is a 150hp Yamaha 2001 w/carbs not EFI, 2-stroke. When he takes off, it takes off good for about 10-15 seconds then dies down and won't go above 3500 rpm(20mph?). Compression on the 6 cylinders were upper left 100psi ml 105psi lb 80psi, top right 80psi mr 80psi br 100psi.... according to what I've read, with a yamaha the compression between cylinders can very by 30psi. We sprayed some carb leaner in and it ran pretty good for a few seconds then died back down. We only run high octane fuel through this motor, and the spark plugs aren't fouled up with carbon, but had a little oil. With a 2-stroke is that common? Any ideas on what might be causing this. I haven't torn into it yet myself, but figured I would get some input before I started.

    Thanks for any help
     
  2. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Do a good decarb and do it soon. The compression should never be over 10% to 15% difference between cylinders. It sounds like it is going into slow mode when it usees all the fuel in the carbs so you may have one that is stopped up. Check all your lines to it and take the air slincer off and put it in the water and when it starts to shut down squirt you some pre mix in the throat of each carb one at a time and when it speeds up that will be the troublesum carb. If the carb is putting enough fuel to it it will bog down like it is flooding on that carb so give it time to clean itself out.

    Get you a can of seafoam and add it to a gal of fuel and run it through that engine. After about 15 min of running take it to the dock tilt it up and add some seafoam to each cylinder through the spark plug holes.
    Find you some thing to do for about an hour and then go back and run the rest of the gal of fuel mix with the seafoam in it and run it like you just stole it and trying to get away


    When you get thru clean the plugs real good or add new ones and see what that does. Be sure to let me know.
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Compression on Yamahas should be close to equal on port and strbd cyl's, they can vary up and down some, but not much from one side to the other.

    Fuel pumps are very important. Be sure they aren't leaking into the crank case. it's straight gas and will wash the bearings of oil and blow the engine. They operate from crank case pulses. You may only have one.

    Loose the high octane gas. If you've read much, you'll know that 2 strokes are designed to run on 87 octane. Your wasting your money and hurting the engine. It may be too late. High octane gas is designed to have a more complete burn. 2 strokes need that unburned fuel of lower octane, to keep head temperatures at a minimum.

    If things can be fixed, next you should have a fuel water seporator on the boat for your on board tanks.
     
  4. srjones

    srjones New Member

    Messages:
    18
    State:
    midwest city, ok
    thanks I'll try that tomorrow. We changed out the fuel pumps today. both of them wouldn't hold on a vacume test.