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  1. #1
    Member
    Join Date
    Feb 2011
    Location
    Benton, KY
    Posts
    1,041

    20hp Four Stroke Top End RPM's

    2013 Mercury/Tohatsu 20hp four stroke loses a few hundred rpm's at wide open throttle after 3-5 minutes running WOT.

    Motor starts instantly and is fine (no misses or hiccups, no sputtering), idles fine, runs low speeds fine, accelerates instantly just fine, WOT is also fine but after 3-5 minutes at this WOT it starts to gradually lose a few hundred rpm's/2-4 mph's even though the throttle is still held at wide open.

    Choke is not engaged. No leaks in fuel lines, fuel filter, or carburetor. Fuel filter was new in the spring of this year. Fuel always has Seafoam added at 2oz. per gallon. I ran the motor off of the existing portable gas tank in the boat and even off of a new spare fuel tank and hose that I keep in reserve if needed for a long day. Fresh fuel with no water in both fuel tanks. Motor acts the same at all speeds when using both tanks. Carburetor seems to not be the issue, I assume. Boat/motor always stored indoors (50*-70*).

    What's my problem? (Slightly weak fuel pump?)

  2. Member
    Join Date
    May 2011
    Location
    Spangle, WA
    Posts
    6,180
    #2
    You might try posting in the 4-stroke forum 3 below this one.
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax


  3. Member
    Join Date
    Feb 2011
    Location
    Benton, KY
    Posts
    1,041
    #3
    Thanks Silver Fox. Will do.