Yamaha 50hp outboard

The carburetors are in desperate need of some PROFESSIONAL attention. They all stop up after sitting for that long.

water pump impeller failure check tell water outlet for flow
blocked water inlet holes
corroded plate in the block between coolant and exhaust allowing exhaust gas into the coolant
corroded cylinders

the exhaust ports start from the side of the engine block 2hp -90hp then v4 and v6 and v8 are between the v blocks ! from there they go down the leg unit , top rear of leg have an outlet for tickover then the main outlet is either through the prop or above it on small or old type engines !

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

Check pump housing and plate for wear,make sure aluminium housing not corroded under plate. Suggest fitting electric drill to drive shaft and emerse lower unit in bucket of water.make sure drill doesn't get wet.is motor going into gear,maybe splines are rusted off in crankshaft,could also have holes in inner exhaust side plate

put a water pump kit in it

First thing to check: Disconnect the tiny hose between the check outlet and the engine. Disconnect it at the engine side.
With an airgun, blow in the check hole from outside to engine side.
With an airgun, blow out the engine connection.
Start the engine, check waterflow out of the engine connector. If water, reconnect the hose and check the water at the checkpoint.
If still no water at the engine connection: replace the impeller!

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.