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1998 Nitro 640lx 75hp Tracker Top End Rpm Loss

Thread in 'Motors & Props' started by Pete, Mar 9, 2019.

  1. Pete

    Pete New Member

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    About two of three years ago I started losing top end RPM and have no idea why. This is a traditional carb motor which I have taken to two different service dealers and they say the motor is running fine. I have a Stilletto 21in stainless steel prop on the motor and it used to run 5000RPM and a solid 45 to 47MPH on the speedometer. I was told compression is fine, I have change the plugs, changed the fuel filter, had tune ups at the shop and run fuel cleaner through it. I also at one point tried a new Laser II 22in pitch prop which made no difference.

    I can only reach about 4700-4800 RPM and only a little over 40pm? Are there any suggestions of why this might be occurring? I am at a loss as to what to try without spending too much money. It almost sounds like at times the motor wants a little more fuel at top end but other than that the engine runs very srtong. It is a little cranky at idle and to fire up but it is an old school carb motor.
     
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