my mc16 stinks of fuel, not massively but enough.

when i come back from a ride, i turn the tap off.

i checked for leaks and i didn't see any.

i have a sneaky suspicion the choke is not working cleanly as the spark plug is black fouling alittle on edge of plug (brown-tan on the electrode), the operational feel of the lever is like it only opens when fully pulled but doesn't give me the feel is returning fully when closed.
or
because i just bought the bike recently i'm wondering if it has been stood about for ages and the float needle is past its best. does this sound like the source of the problem.

the air box is clear, the tap is turned of and the tank breather pipe is clear too. what i have notice is that the previous owner has fitted an extra long fuel line to the bike probably making access easier (how long is the pipe normally) and could this be the problem that their is too much fuel still evaporating after i turn the tap. should i run it empty before stopping or just clean the carbs up.

is this normal on the mc16? thanks