1995 merc 40 hp wont plane, 3400 rpm

boat ran great, then suddenly would not run over 4200rpm, down from @5200. barely plane. I eliminated fuel system fromexit of cowl, then all nee fuel lines and clamps to carbd. rebuilt carbs and fuelpump. good compression. new plugs, stator, switchbox. all grounds good. all connections good. starts, idles fine. last trip was down to 3400 rpm

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Jul 26, 2020
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starstarstarstarstar 		99 Merc 4 stroke 40 hrspr
by: Sooner be sailing

Ours is a 4 stroke 40 horsepower, still no solution, been to three knowledgeable mechanics now and no solution. Carbs rebuilt, all electrical researched, fuel lines and tank all new, nothing left to change but the whole motor. The last guys said low compression is the problem but this motor has sat more than run all its life, low hours, so we dont believe the cylinders are shot. Have fogged it to stall each year at end of summer and run the system clear of fuel for storage.
Jul 09, 2020
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starstarstarstarstar 		motor bogging out at higher speed
by: Sooner be sailing

Our club has paid about $3000 to service our 99 Merc and after all that suddenly a third mechanic says the compression is too low for it to run higher RPM. It starts fine, idles fine but only runs to about 1/3rd throttle and then stalls right out. This motor has very low hours on it, we cannot believe the cylinders are worn out. Still think something else is going on. They have changed all the fuel line and tank, plugs, coils and more. It will run all day at lower rpm.
Jul 09, 2020
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starstarstarstarstar 		Did you Fix Your 3400 RPM Issue?
by: Anonymous

Did you solve your problem? I have same issue with my 150HP 2-stroke Blackmax

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