CHops,
on a 25 of that vintage I would be very surprised if it had anodes within the cooling jacket.
Most likely one of the reasons why they are so good at rusting out the exhaust manifold/baffles
To be honest chops on smaller 2 strokes for my use i will usually remove the thermostat altogether. They will run a little cooler but up here thats not an issue and the thermostat by its very nature limits good flushing.
Pilbara that is some good going build up you have in your cooling passages. I would be yanking the leg and power flushing the system from the draw tube with those anodes and the thermostat out to flush that stuff. Perhaps even consider some Salt-X or equivalent?
S

