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F350 Hesitation RPMs Drop at Higher Output 4000-5000RPM

Matt WhiteMatt White Satellite BeachPosts: 6 Greenhorn
I'm having a high output issue currently with my F350. 69 hours since last flywheel replacement.  Most recent operation timeline is as follows...  Ran boat from Satellite Beach to Stuart (outside) last Friday. Fished (ran it) all day Saturday.  Fueled up in Manatee Pocket (she took 52 gallons) and ran back up to Satellite Beach (~70 mi run) in the intracoastal Sunday.  On the way home, ran it in a 4800-5000 RPM range majority of time (approximately 2 hours). Towards the end of the trip home the motor would hesitate and behave like it was coughing (35 gallons burned).  When I reduced RPM to 4000, all was smooth.  Total round trip mileage last weekend was (~160-170 statute miles).  This weekend ran at 4000 and she isn't happy.  RPMs drop and she tries to get back to 4000 but just cant do it.  Drained fuel from water separator and fuel is clear.  Changed the Water Separator anyway and changed the Under Cowling Fuel Filter also.  NO LUCK.  Lower RPMs run smooth.  Higher RPMs she isn't so happy. Noticed a reference to Primer Bulb in earlier posts - mine remains squishy on plane.  Plan on changing that today.  Any input / solutions to similar experiences would be appreciated.  Happy Father's Day gents!


  • Frosty1Frosty1 Posts: 140 Deckhand

    I'm not  a mechanic, my guess would be fuel issue, check all hoses from tank to engine including bulb, hopefully not a tank issue.

    Hope its an easy inexpensive fix

  • Matt WhiteMatt White Satellite BeachPosts: 6 Greenhorn
    Thanks Frosty1. Switched out the primer bulb, no luck. I'll keep ya posted.
  • Matt WhiteMatt White Satellite BeachPosts: 6 Greenhorn
    I changed all three, Water Separator, Under Cowling Filter and Primer Bulb. No luck. Took it in and plugs got changed. Mechanic ran it for 20 minutes after plug changout up too 6100 RPM and claims problem solved. Pick it up today.
  • KlingerKlinger Posts: 1,889 Captain
    Might be the high pressure pump screen inside the vapor separater tank. It can blank over and restrict fuel flow to the injectors 
    In my many years, I have come to a conclusion that one useless man is a shame,two is a law firm, and three or more is a congress.-- John Adams
  • Matt WhiteMatt White Satellite BeachPosts: 6 Greenhorn
    Swapped out the old Spark Plugs for new and problem solved.
  • BarrellBarrell Posts: 1,238 Officer
     I own a lot of things with motors. Over my lifetime Ive learned to change plugs first as its cheap to do.
  • 4WARD4WARD Cross Creek,FLPosts: 1,662 Captain
    F115 developed similar problems yesterday.
    Starting with draining fuel and changing all filters, just added plugs to the preliminary list. THANKS
    "I hate graveyards and old pawn shops
    For they always bring me tears
    I can't forgive the way they rob me
    Of my childhood souvenirs"... John Prine
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