Sounds like its probably rich at idle then starts to foul the plugs. When you bump the throttle it clears up because you are not running through the idle circuit anymore.

Sounds like you've went thru the ignition system.

You need to find out if when it starts running like crap, is it dumping fuel in the engine? Or lacking fuel? Possibly a fuel pump issue? Needle and seat or float sticking?

You really kinda need to diagnose the problem, when its acting up. First you need to check to see that you have sufficient fuel pressure from the pump. And see what the carbs doing in terms of fuel at idle. If the fuel system passes some checks, you can move on to the ignition system.

You'll wanna check to be sure you have full voltage to the coil, and other ignition parts with a multimeter. if you are good there, i'd check to see what cylinders are not firing. What I used to do, and you'll need to be careful in a boat, with fumes and what not for this. But when it acts up, you can loosen the plug wires at the cap. So they are on, but not fully seated. Take a test light, hook the alligator clip to ground. Then, with engine running, take the test light probe and stick it between the boot and terminal. The spark from the cap will jump to ground (test light), and if that cylinder is firing ok, the RPM will DROP. If that cylinder wasn't firing properly, the RPM will stay constant. You can go around the cap and check all 8 cylinders pretty quickly this way.

Thank You for all the responses! Of course today was one of the days it would not act up. But I did a full compression check, all cylinders are reading around 145 PSI +/- .. Did a leak down test, and all looks fine. Will be on to the next of your suggestions tomorrow! Thanks Again!!