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  1. #1

    Default 2003 yamaha t8 4 stroke running poorly

    I have a 2003 yamaha t8 four stroke that starts and idles fine but when you throttle up it bogs down. I thought dirty carb so I cleaned it twice and the same thing happened. Fuel pump is fine with 4 lbs of pressure. I put a new coil on it and still the same. A friend of mine had one he wasn't using so I exchanged all of the parts I could think of...(working carb, power pack, coil under the flywheel, flywheel) you name it and it runs the same. Compression test comes out good at 160 lbs with a 5 lb difference between cyl. Ran a leak down test and everything checks out..no leaks.
    All I can think of now is camshaft or valve lash... just doesn't make any sense.


    Have any idea's?


    Matt

  2. #2

    Default Re: 2003 yamaha t8 4 stroke running poorly

    I am having the same issue with my 9.9. starts on forst pull and idles great but when you gas it, it bogs down. It feels like maybe the timing is not advancing?? someone said that is the oil pressure is low it may retard the timing during high idle, but i am getting a green oil pressure light. I also heard that if the fuel pump diaphragm leaks fuel into the oil it would cause similar issues. I am going to replace the diaphragm this week and put in a new oil pressure switch. let me know if you figure out your problem. good luck.

  3. #3

    Default Re: 2003 yamaha t8 4 stroke running poorly

    Quote Originally Posted by captainkeene View Post
    I am having the same issue with my 9.9. starts on forst pull and idles great but when you gas it, it bogs down. It feels like maybe the timing is not advancing?? someone said that is the oil pressure is low it may retard the timing during high idle, but i am getting a green oil pressure light. I also heard that if the fuel pump diaphragm leaks fuel into the oil it would cause similar issues. I am going to replace the diaphragm this week and put in a new oil pressure switch. let me know if you figure out your problem. good luck.
    I have not heard that from anyone. What year is your 9,9? My oil light is fine but I unplugged it anyways just to be sure. Also I've been told they don't have an advance. I figure if they do it all created in the power pack. I took the fuel pump apart...there is not much to them. It squirts across my driveway and tested at 4 pounds, I don't think that's the cause. Pretty bafold on this one.

    Does anyone know what each coil does under the flywheel? There are what I believe 2 charge coils (what do they do) and one lightning coil (what does it do) I ran ohm test but had trouble getting any voltage test that was suggested in other blogs.

    Any help would be greatly appreciated.

  4. #4

    Default Re: 2003 yamaha t8 4 stroke running poorly

    I pulled the valve cover today and found the valve clearance was off. I adjusted this and got the power back. Maybe check yours. goos luck

  5. #5

    Default Re: 2003 yamaha t8 4 stroke running poorly

    Quote Originally Posted by captainkeene View Post
    I pulled the valve cover today and found the valve clearance was off. I adjusted this and got the power back. Maybe check yours. goos luck
    Pulled the valve cover off tonight and everything's appears good. Can't find my feeler gauges so I will go buy new ones tomorrow. They are not to tight and all seem to be close to spec by feel. I guess we will see tomorrow...I did note they are a tight tolerance.

    I find it hard to believe that this is the problem.

  6. #6

    Default Re: 2003 yamaha t8 4 stroke running poorly

    Quote Originally Posted by saltchuckmatt View Post
    Pulled the valve cover off tonight and everything's appears good. Can't find my feeler gauges so I will go buy new ones tomorrow. They are not to tight and all seem to be close to spec by feel. I guess we will see tomorrow...I did note they are a tight tolerance.

    I find it hard to believe that this is the problem.
    Ok pretty much looked at everything and or changed over parts that I know works. I guess I stumped everyone here. Valves adjustments were almost perfect but now they are even better. The only thing I can think of is some kind of internal issue or a crack in the intake manifold that I cant see or hear. Anyone know how to hook up a intake manifold gauge on a T8?

    I think I'll just part it out.

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