The later Clamshells abandoned the thermostat & poppet valve. Whether for this or other reasons I don't know.
Mine has been rebuilt like that to ensure it's longevity, and yes, it idles like a dog now when cold compared to the pre rebuild.... but as I don't spend very long pottering about at idle I can live with that!
Admission time - I have only ever flushed an outboard twice in about 6 years .... granted for 5 years they always had a fresh water river run for the first & last 10 minutes of use , but given what the majority of engines get treated like ( generally used and abused) I'm not going to worry...
I just look across any marina / harbour at whats out there to make myself feel better.
I guess they had a run when they got serviced each year, but only in the last six months have even owned a set of muffs !
Thanks DryRun , happy to be of service. i think as the boat is on a mooring it'll only get flushed twice a year. I wondered if flushing for say an hour would shift any build up or is it permanent once it's in there ?>
In my experience, corrosion salts do not readily dissolve in water and I always find a build up of salts around my anodes even after flushing. I think the flushing really just attempts to dilute the concentration and reduce the amount of saline water being left in the passages. I guess the first few minutes of flushing are the most beneficial and critical. After that, you may soften and flush out a few crystals but not much overall. All IMHO of course...
Every time I use the boat if I can get near a hose with some pressure. With a flushing port I just plug it into the hose and tidy the boat up while it is flushing. Probably wouldn't be as anal if I had to use muffs and start the engine up. I try to do it striaght away while the engine is hot and the thermostats are still open.
Don't really know if it does much good but at least I feel like I tried!
So what happens when the hose pipe ban comes in , Does that include marina and yacht club hoses,
Down ye old yard we used to have a 40 gall water tank and we'd just let people use it when there finnished playing for the day,
Maybe other yards could offer this, Simply back her up, Dip engine in up to anti cavitation plate and run for just a minute or two. Plus you have the option of additives in the tank.
Could always collect the waste water from under the engine and use it to wash the hull. Waste not want not!
Exaclty what I did when I had a jetski - squirt of soapin a bucket, stick the bucket under the outlet and run the engine for 2 minutes - end result a lovely warm bucket of soapy water to wash down with
I have read with interest flushing or not all i will say is and i believe most if not all the dealers will agree that regular flushing is advisable especially in salt water as most of the dealers on this site will tell you, we have all seen the damage it can do, basically preaventive maintenance , when i used to work at the distributer we had parts that we showed in the service school that were blocked solid with salt, yes i know what people have written heard it before.
, Does that include marina and yacht club hoses, 
Plus you have the option of additives in the tank.
