What is this rust like matter..anyone?

FIrst of all, welcome to the forum Paul.

Well, maybe it is just chain lube mixed with dirt, or something. That would be the best and easiest thing for you. That is probably what it is...hopefully. If it was your coolant looking rusty, read on....

I have seen firsthand an engine pumping corroded (looked like mud almost) water in it's cooling system. Have you popped the cap on your radiator and looked at the color/condition of the coolant? If so, you may have corrosion in your cooling system. This could have happened from using/leaving coolant in your motor until the coolant was broken down enough to allow impurities in the water to form rust/scale. This can be fun to get out. IF, this is your issue, you could first try and FLUSH, FLUSH, FLUSH, your cooling system with a garden hose until all of the rust/scale if out of it. Then flush it with distilled (or de-ionized is the best to use) water until you get all of the tap water out of it. In extreme cases, then get some rust/scale remover for cooling systems from an automotive store, pour that in, with the distilled water/antifreeze, run it for 2-3 days to allow it time to remove the rust/scale. Drain that out, flush it again, and again, then put distilled/de-ionized water with antifreeze back it in. This still might not get out all of the scale. My old Ranger had this problem, and it was a biatch to get all of the rust/scale out of it....of course the Ranger has a cast iron block as well, and our bikes do not. Still, check the condition of your coolant, and it if looks nasty/rusty/scale, flush it well, and put the good stuff in.