Steve.... The reed plate (leaf valves) consist of many finger type flapper leaves so if one was blocked shut, I doubt if it would be noticable. On the other hand, if any of those leafs were jammed open via any foreign article, that would interfere with the vaccum needed to drawn the fuel in.... this type problem would show itself in the form of fuel being blow out the carburetor throat on every down stroke of the related piston.
There are four high speed jets, two to a carburetor, one obviously for each cylinder. I am assuming that you have removed all four (4) and cleaned them manually with the copper wire that you've mentioned. If you haven't cleaned all four, do so... if you have, there's always the possibility that some debris has broken off with a fuel line (whatever) and is interfering with a jet.
Do the two finger test. With the engine acting up, stick two fingers in the carburetor throats, one carburetor throat at a time of course (not the complete carburetor at the same time), and note the response. A drop in rpm indicates you've caused a increase in the fuel quanity which is flooding the cylinder BUT if the test causes a cylinder to increase the rpm and smooth out... you've found an offending carburetor.
The problem to me (without actually being there) spells carburetor. You asked in your second post (actual #3 above) "why am I getting fuel to left bottom and not the right?"
Many boaters have the habit of (for the winter) having their engines tilted up and swung to one side. That results in two of the high speed jets being higher than the other two with the result being that two jets are most prone to fouling. Which in turn results in one bank of the engine running lousy if it fires at all. This is of course assuming that the compression and spark is as it should be.
You indicate that the rig is doing about 2 mph at full throttle. Has this improved? This would have to be more than one cylinder failing. The compression you state of 115 psi on all cylinders is great, and you've indicated that with the spark plugs removed that the spark does jump a 7/16" gap. These two areas, in that condition, would be perfect. Too bad you're not close by.