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  1. #1

    Default low rpm at wot 1985 50hp Mercury 2 stroke 4cyl

    Im dealing with a problem and to sum it up..I cant get past 3000 rpm at wot.motor runs good .. starts well.. and idles ok, doesnt break up no smoke.just serviced carbs.. cleaned by mechanic, and put in all new gaskets and fuel pump diaphram etc..put in new fuel line assembly and primer bulb.had it out on lake today (and past 5 times).. cant get it to higher rpms..motor sounds healthy..i should note that its a 17ft fiberglass 1960 aristocraft..motor is 20in shaft.. and i have the stabalizer plate level with the bottom of the boat.even tried a hydrofoil..thinking it was a weight issue and not getting to plane.did a compression test...120psi on all 4 cyl.new plugs,fresh gas and proper 50 to 1 mixture.when i had the carbs off.. i checked the butterflies when throttle was pushed all the way forward.. and they were wide open.some history..i bought it used 4 years ago.had a new stator put in by a boat guy...and then it would start .had one good day.. (note: i only take out in the summer.. maybe 6 times last year)so i know it has capability with my setup to achieve over 20mph.boat not getting to plane.. and only doing 8mph..ive read it could be exhaust build up ..ive heard about safe modes that limits your rpm's ..but im looking for a poor mans approach before i take to a boat mechanic nearby..any suggestions would be greatly appreciated..thank you.
    Last edited by tkowalchick2; 06-01-2020 at 09:19 PM.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,751

    Default Re: low rpm at wot 1985 50hp Mercury 2 stroke 4cyl

    Try a different prop with a lot less pitch.

    Jeff

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