Having seen the carburetor with the dirty float bowl earlier in this thread, I can't resist talking about the one I just found this morning. I bought an old Honda GXV120 engine yesterday, because I wanted a few external parts from it. The seller (on Gumtree) said that it wouldn't start, it might be something simple, he didn't know. After stripping the bits I bought it for, and using them to complete and test another engine, I noticed that the air cleaner element and the interior of the filter box were oozing with black engine oil (it was far too thick to drip), and the operating lever for the coupled choke had been bent out of the way so the choke didn't operate. This made me suspect it had been burning a bit of oil. The sump wasn't dry - it had about 20 ml of thick sludge in it, but no actual liquid oil. However I don't think the oil burning was the main reason it wouldn't start. This morning I took a look at the carburetor:
[Linked Image]

The float bowl was more than half full of that black granular stuff in the picture, and if you look at the underside of the float, you'll see it was being held up by the pile of stuff so it couldn't lower the needle and let fuel in. I suspect that was the immediate cause of it finally giving up the ghost. I'm not completely sure of that: the idle mixture screw was missing as well, but that shouldn't have prevented starting. Incidentally, the bore and crankpin were worn far past Honda's service limits, and the top piston ring had a gap of 5.58 mm. The valve seats had worn considerably, and the keyhole valve retainers were worn to the point where they seemed to be at risk of dropping the valves. The whole cylinder block, head and crankshaft all had to be scrapped.

That poor Honda was like a loyal old dog that stays with its master even though he abuses it every day. If it had just quit running ten years ago instead of recently, it would have been in a lot better shape when I bought it, and the previous owner would have avoided producing a vast amount of blue smoke.