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1993 yamaha 25hp 2 stroke engine not running well or at all

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  • 1993 yamaha 25hp 2 stroke engine not running well or at all

    Hi I have been having issues with my 1993 25hp yamaha outboard 2 stroke .

    I have owned this engine for 3 years now and for the most part it ran perfect aside from a slight stutter at idle .

    this year my first outing the engine fired up and started stumbling at idle and stalling . I then ran it wide open across the lake to my fishing spot and had no issues . From there it. Just kept stalling while *****ing till it stalled and wouldn’t start . After about 15 minutes I got it to fire back up and went straight home with it bogging and wanted to die . During this time I was playing with the choke which appeared to help but I can’t be certain as it still wanted to die .

    I went home took the carb apart and cleaned it ( it was very clean to begin with ) , i reassembled and started the engine and it would do the slight stutter as it usually did the previous years . I looked into the air mixture screw and found it wasn’t properly set so I adjusted it to spec and it ran smooth .

    i took it out on the lake and had absolutely no issues ran the best it ever had and I thought I fixed my issues . We’ll I was wrong the following day I Go out fishing again and it would start and stall . After a few attempts it was running fine so I went WOT and noticed intermittent power loss so I slowed down . The engine was running rough at idle and then stalled , after this the engine didn’t want to start and after 15-20 minutes it fired up and ran rough . This happened 2 more times before I made it home .

    This morning I fired the motor up and it ran a few seconds before stalling , I did this three times and then it just stopped firing .

    i disassembled the cards again and everything looks clean with no obstructions .

    im hoping someone might have had a similar issue and could help . Here is a list of things I have checked

    fuel tank is venting properly
    fuel bulb stays hard when pumped
    checked all fuel lines for obstructions
    checked fuel filter
    cleaned carbs thoroughly
    compression is 100psi on both cylinders

    there is spark and the plugs are slightly wet After a bunch of pulls .

    I have not tried new spark plugs yet as I live in a small town and unfortunately don’t have access to them so I will be getting new ones on Monday when I travel into the city .

    I attempted to check the ohms on the coils and sometimes the numbers would bounce around on the cdi connector side and one coil would show a k with the ohms symbol and the other coil would show a m with the ohms symbol

    I think the multimeter is one that changes automatically however I have little experience with these .

    the output to the plugs showed between .3 and .5 fairly consistently however it would bounce around to higher numbers sometimes .

    im sorry for the long post I just wanted to give as much information as possible and hopefully I can get back to catching them walleye .




  • #2
    Twin or single carb? The exact model would be helpful.

    I would take carbs off and clean again, with an ultrasonic cleaner if possible. The idle circuits on those carbs are very small and hard to get clean once they get plugged up. Probably rebuild fuel pump on the bottom carb as well. I have the same engine...

    Make sure you dont have dirty gas and plug them up again.

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