How’d you clean them? Just changed the chain on my bike - had to lift the small sproket cover…and looks like someone treated the bike as a dirt bike at one point. Managed to get a bit of it off… So I think I’ll pencil in a end of winter clean on it. But what’s the most effective way - degreaser and a tooth brush? What about by the rear suspension; how to clean that; pressure washer?
When I cleaned the area around the front sprocket on my 125CBF I used paraffine, tootrbtush, toothpicks and tissues to get to the hard to reach places. Worked for me and had a clean sprocket area.
I had to do this on the race bike. Stripped it down and degreased it then replaced/regreased all the bearings and put it back together, looks new 
+1 paraffin
WD40 and cloth.
If you’re talking about chain fling inside the front sprocket cover scrape out as much as you can with a flat bladed screwdriver. its not worth doing a proper cleaning job because the area will soon re-fill with chain fling. If you really want to see it properly clean before installation then finish the job with a short blast of carb cleaner, brake parts cleaner or, as above, tooth brush applied paraffin followed by a not so oily rag. As soon as your riding again chain fling will will soon enough re-fill the cavity around the front sprocket.
If you're talking about chain fling inside the front sprocket cover scrape out as much as you can with a flat bladed screwdriver. its not worth doing a proper cleaning job because the area will soon re-fill with chain fling. If you really want to see it properly clean before installation then finish the job with a short blast of carb cleaner, brake parts cleaner or, as above, tooth brush applied paraffin followed by a not so oily rag. As soon as your riding again chain fling will will soon enough re-fill the cavity around the front sprocket. National Treasureits actually not that much chain fling in there (I use the SDoc stuff, which appears todo what it says on the tin...) But there's a build up of mud and old chain fling grease, so wanted to find the best way to clean it - I used some of my chain cleaner and go a little bit off; but it was very sticky. Seems some cheap tooth brushs and appropriate solvent is the way to go.
It will be chain fling, black rubbery chunks of gritty, greasy, oily stuff.
Flat bladed screwdriver to scrape off most of it followed by an assortment of brushes, rags and paraffin. As before for a perfect eat your dinner off it finish off with carburettor cleaner or brake parts cleaner and a buff with a clean rag. Inspect it again 4,000 miles later and the black rubbery chunks of gritty oily chain fling will be building up nicely. Note you get more chain fling around the front sprocket than anywhere else because of the higher centrifugal force.