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Greetings, I have a 1993 OMC 351 engine in my 245 Vista. At three quarter and above throttle I'm experiencing what I call a "miss" that is easily felt. When I ease back on the throttle this miss goes away. Any thoughts on where I should start looking for root cause? The boat is new to me and I've only had it out 4 times so far this year, but each time it has done it. I reached out to the previous owner and he claims that he has had no issues with it.

Fresh fuel, no water.
Replace fuel filter
Fuel pressure and flow
Ignition- do a tune up. Distributor, cap, rotor, wires and plugs. Points also if it's carbonated.
Vacuum leaks

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1996 Four Winns Horizon 200DLX
Engine VOLVO PENTA 5.O 50FAPNCA
Transom Volvo Cobra SX 3868388

Update:
My mechanic replaced the fuel filter and discovered a large amount of water. So he drained the tank, put fuel additives and about 10 gallons of fresh gas in it and states that the carb looks just fine and it runs fine at the shop. I take it out, put another 25 gallons of marina gas in it and under load it still misses/hesitates. Mechanic doesn't seem interested in working on it so I did the following: Changed the plugs (which was a total pain in the rear end - changing them but even finding the correct size plug was an ordeal). Replaced distributor cap, rotor and coil. Took it out last night and seems to run a little better however around 3400 RPM it misses/hesitates but stops doing that as I increase RPMs. It runs fine at WOT. Regardless if I slowly increase RPMs or punch it, it hesitates around 3400 and then goes away. Another observation to share is that when it misses/hesitates the oil gauge bounces around but stays around 40 when running fine.

So whats next - change the distributor itself??

Check your charging voltage if you see a gauge bouncing around like that. You may have low voltage to the coil that shows up with that load of being at that rpm. So if you are not between 13.7-14.2 with the engine running go check and clean all the terminals starting at the battery, then to the starter then to the alternator. I had this with mine. Any time I would hit the trim button the engine would stumble. So I went over every connection including the trim relays and that hadn’t happened in years. If you have wing nuts on the battery terminals get rid of them because they get loose and cause low voltage issues. Use locking nuts or have new cables made up with proper marine battery clamps. Don’t forget to clean the engine ground that the neg batt cable is connected to...if your batt cables are original I bet they are all corroded inside.

How did the plugs look? Also not a bad idea to check the resistance of the plug wires. Should not be more than 1,000 ohms per foot. If so replace them.

If this is not it then I suspect a carb problem...what carb do you have? Holley 4160?

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Interesting point about the voltage. i didn't notice the needle bouncing but I did notice that it only shows about 12 amps (less when I turned lights on). I do know that the alternator was recently replaced. Along with that thought, one of my (relatively new) batteries seems to be draining to the point that I need to switch to "both" batteries to start the boat. Even though they appear in good shape, I ordered new spark plug cables today because I do not know when (or if) the current ones were changed.

a couple of the plugs had a petroleum smell to them. I doubt that they had been recently changed or ever changed for that matter. They were Motorcraft plugs that are no longer available.

If it reads 12v with the engine off that’s ok but when running it should be 13.7-14.2V

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Took it out today and its still hesitating at 3400 RPM, runs fine below and above that. Volt gauge at just above idle is 12 and at WOT its only 10-11 (gauge does not bounce around when running). My Number 2 battery reads 12 volts but doesn't have enough juice to start the boat by itself. I didn't have that problem a month ago. Both batteries are relatively new. Going to change the belt to the alternator in the next day or two.

Update: replaced alternator and the hesitation at 34k is gone! Volt meter shows about 13 volts at higherRPM, only 11 at idle. Is that normal?