Plainly understand that's impossible to flush OB's with fresh water after use. The issue is that moored OB's on salt water use will collect thin salt layers one on top of the other due to hundreds of hot/cold cycles when in use. Remove boat from water and flush each OB with Salt Away Product poured on barrel for some time, see if this product works as stated. Works OK on new OB's flushed regularly, will do its homework right with old ones, who knows ?
As we don't have Salt Away product available, when having those issues, attach a flush plug on my OB powerhead, remove thermostat, put cover bolted back in and connect direct to a water hose that delivers high water pressure, let flush for at least 15 minutes.
To illustrate better, this is a salt water used OB with 600 worked hours flushed for 10 minutes after each outingt on muffs & high water pressure. Still forms salt layers throughout the entire water passages with use. So if dealing with salt, can't possible win the battle LOL!!
Exhaust Cover.-
Combustion Chambers.-
Other option depending on clog/crust condition is connect a Karcher Washing Machine set at lowest pressure to flush port and flush at a much higher water pressure for 10 minutes. See if both procedures can be done while boat rests next to a pier provided that those OB's count with a flushing port on the inside or outside of OB.
If both options which works opt for me doesn't work properly, must remove cylinder head, exhaust cover from powerhead, spray shots ofy pure vinegar on water passages, let soak for some minutes to desolve salt properly, then mechanically remove with a thin wooden sushi stick formed salt layes/crusts as not to scratch internal water passags that will collect salt back again very soon if severely scratched.
Happy Boating
