it sounds like you have checked or changed all the major things it could be so theres not much left to check really.

2 things you could try.......

take off the air filter and whilst someone is cranking the starter, gently push down on the metering head flap (not alot otherwise you'll flood it !) If it starts then the problem could well be an air leak somewhere.

secondly, if that dosent work, look at the multiplug which plugs onto the dizzy, check all the connections etc and give it a little wiggle see if that makes any difference.

cheers, Duncan