How about going up a couple notches in the heat range of the plug. Also, gas stabilizer of some types leave soot. Good luck!

My carb has (4) One for (each) Primary and One for (each) Secondary. You can also remove them and spray carb cleaner in each hole. Then spray carb cleaner into the air bleed valves. Make sure when removing idle mixture screws not to loose them cork o-rings which prevent the screws from vibrating loose. I'd check that you didn't blow your power valve also.

Odds are, if the boat was running fine when you put it away, you probably don't have to start screwing with the carb (yet). Before you do anything else, as was said before, make sure your choke is opening fully by taking off the air cleaner, and observing the choke valve. Then, run that old gas out of there. Especially BEFORE you start turning screws! New gas sucks, and even with stabilizer, I've had engines act tempermental until I got some fresh gas in there. Yes it is possible that something got gummed up or stuck over the winter. I had this happen to me last year. My boat was running real rich, and when I removed the air cleaner, and took a look down the carb, I saw raw gas pouring out of the boosters (Rochester). Turns out the float got stuck. A simple fix, and 15 minutes later I was good for the season. If all else fails, then you might have to start adjusting. My point is..Keep It Simple!

Yea its real hard to count the number of turns on those idle screws. Speaking of getting gummed up. I never heard of those air bleeds getting gummed up either. NOT!

I Will start with the choke and go from there tomorrow. I will also spray choke and carb cleaner. Also a good time to blow through a tank of gas, maybe that is the culprit too. Is there anything I can do to tell if the float is working properly without tearing into the carb??

Get yourself some clear float level sight plugs to check float and fuel levels.

I'm not saying that it's difficult to turn the idle screws, I'm saying if they were ok last year, why would they be out of adjustment this year? Gremlins???
I agree with checking the float levels. They can stick. If a float is stuck, and dumping gas, you might see gas coming out of the "J" tubes or the boosters. If you look in the carb while the engine is running, and see raw gas dumping in from anywhere, something is wrong. There are other things that can cause a rich condition, like a ruptured power valve (Holley), dirt lodged in the float seat, etc. If it's dumping enough gas to foul the plugs, I can't beleive an idle mixture adjustment alone would cause that. Especially if no one touched it while it was in storage. I'm just telling you what I would do before making any major adjustments. I've been working on cars, boats, motorcycles, and electronic equipment for almost 30 years.
Some professionally, some as a hobby, and anyone who has any troubleshooting experience will tell you, Work systematically starting with the easy stuff, then work towards the more difficult things. It's always worked for me.

Idle mixture screw if turn out too far will cause a rich mixture and dump fuel into the carb causing the plugs to fowl during long idling or traveling through no wake areas. A stuck choke or improperly adjusted float level will cause a similar result. Power valves can easliy be ruptured from a backfire. There isn't just one answer it could be any of the above. I'd rather have as many options as possible instead of trying one thing one day and then another the next day. Beside getting "CHECKROCKET" back on the water and everyone learning from the technical board is what forums are all about.

I am heading to the lake today and see what I can do. I am hoping for success. If its not the choke and I clean everything out. I am going to run the boat for a while and burn off some of the gas from last year, then I guess I will try the mixture screws and some new plugs so I can get a reading, does this sound like a good order.

The power valve was bad on my motor. However I need to get the air and idle mixture correct. I see that I should start at 1.5 turns after seating out. Does closing off the mixture screws to lets say 1.25 make it richer or leaner?? I just want to be on the correct page. Also, I believe before this problem started my HP500 idled at 750rpm, is this what I should shoot for??? Any help would be appreciated, Also where should the large adjustment screw on the throttle side be at. What exactly is this adjusting??