What is the year of my Yamaha 50hp 6H5 L 903842 T

One cylinder may be starved for oil causing the noise your hearing.

Make sure carbs are clean,check exhaust tube isn't blocked,check resistance readings on charge coil,make sure filters are clean,no fuel leaks in fuel line,tank has open breather,fuel connector not blocked.if this doesn't solve the problem could be faulty cdi unit

i have had this on mine and it was a sort of insect that made a mud nest in the small hole and it blocked the hole up ,try poking it out with a bit of wire

sounds like you are going to have to pull carbs off and clean jets also check tank and line for debries

If it has the old points system you will need to set the points also adjust the carburatior screw the screws all the way in and back out 2 1/2 turns then get it to run turn the air mixture screws till it runs smooth. you want it slightly lean then enrichen it slightly, afterword shut the engine down and look at the plugs if they are gray black they are ok. good luck.

Marine stores have a lead lined foam sound proofing mat. You can cut and glue it in place.

this is not accidental, some water is ejected through the exhaust system!

you have bad solenoids.  Replace them and things will be fine.