Regarding adding oil to the fuel tank after adding gas... What I do, is go to the gas station and add an exact, measurable amount of gas, for example 2 litres. Then I know that I need 20ml oil/litre of gas (1:50) so I add exactly 2 X 20ml (40ml) of oil (measured with a measuring spoon I carry around). Then I stir it around a bit with a clean plastic dip-stick which I have. This seems to work quite well. Unfortunately, I think I got some crap in there in the process so I have to re-think my method.
I believe that I have solved the problem of crap in the fuel system, however - because I cleaned every little orifice and hole and nothing's clogged. Here's my new theory... it seems like the bike is starved for gas... i.e. the fuel/air ratio is too lean. If I ride around with the choke pulled halfway, it seems to run fine, or at least much better - it doesn't stall out or anything. SO... when re-assembling my carburetor, I think I messed up the choke cable somehow... does anybody know if there's a way to adjust the choke... so that it's a bit tighter and doesn't let so much air in all the time...? I might have to take the carb apart again and check that out ..... does this make sense? Like I said, the bike will start and run almost perfectly if I hold the choke down.