99 mercruiser 5.0, 2 bbl carb. 22ft wellcraft walkaround. Background....burned out main wiring, replaced, boat started backfiring (popping) under load and wouldn't plane out. Replaced fuel lines, coil, cap, rotor, plugs, wires, fuel pump, rebuilt carb, perko, batteries, drained tank replaced fuel, alternator, somewhere along the line it seemed to clear up. Did one at a time but randomly cleared one day. Took it out and ran it..seemed ok. Next time out did it again, found plugs to be black, changed plugs to original spec (other new plugs were diff brand sold to me by marina) fired right up on muffs and sounded good. Had it out several times now and the same thing happens every time...cold start at dock, fine, idles fine, 15-1800 rpms out past now wake zone fine, power up pops and feels weak until it struggles itself up to plane, after that...fine all day, shut it off to troll with kicker for hours...no problem, jumps up on plane, no popping, no struggling...all day runs great. Take it out couple days later same scenario. I'm lost. Any help would be appreciated thank you. Oh also black smoke for 30 secs to 1.5 mins at cold start but gone for the day after that as well.
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