1989 Mercury 350 5.7 motor acting funny?????

looses power at full throttle, rpms drop and boat countinues to run (poorly) but will not plain out. Then as if by magic it regains rpm???? Have checked and replace everything fuel related but stil having the same problem, (fuel pump, fuel filter, carb all checked and or replaced)... Does not seem like fuel starvation, could something be bogging down the out drive??? Thanks Mike in EL Paso Texas

It may very well be momentary fuel starvation once you get into the secondary throttle bore fuel metering.

Have you looked at ignition timing?
Not just BASE advance, I'm speaking of the Progressive advance and TA (total advance).
An engine that is not receiving the correct spark lead, per RPM, will not perform well.

Mark off your harmonic balancer up to approx 35* BTDC, strobe your timing marks, and increase RPM in increments of 250 rpm or so..... up to 3.5k RPM or so.
Plot this out on paper, and compare it to your OEM ignition advance curve.

You can find the Merc OEM ignition curves here.


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Have you checked the tank for crud in the bottom?

how about the anti-syphon valves?