I would also say it sounds like your flooding the engine. normally as they get older the fuel filler pipe corrodes and rust from it goes into the tank, I would hazard a guess that this will be the cause of your problems. Have a look at the filler neck and if in any doubt replace it, I think stainless ones are available so it makes sense fitting one of them.
Next time is plays up and wont start for a while try removing the plugs and seeing if they are fouled up by excessive fuel, maybe leave them out and spin the engine over a few times without touching the throttle and then put the plugs back in. try and start it.
As for setting the fuel flow metering flap you need to undo the rubber pipe from the top of the metering unit and put to one side, now get a magnet, one on the end of a screwdriver for picking up things is ideal.
Now place this on the metering flap and just move it up and down, you want to feel for any notches in the movement which might indicate wear in the fuel metering valves inside.
Lift the metering flap right up and you'll see underneath is a clip that you turn to adjust the position of the fuel flap in the metering cone. lower the flap down and it should sit roughly inline with the bottom of the metering cone. if it doesn't then pull the flap up and twist this clip from side to side till you get it sitting right.
