misfire Please help

I've developed a misfire changed dizzy cap and leads and now fires on all 4 put wont pull.
When the engine warms up it ticks over pretty much normal at about 1000 rpm and revs up ok while stood still but just will not pull.
I'm wondering whether its something to do with vaccum advance
The only thing not changed is the coil
This happened over night well put it in garage one weekend and the next it had a job to start
Can any one help please???  

Have a look at fueling seems you have done all the ignition . Have you checked the timing with a strobe light ?

Hi thanks for info no i havn't checked timing dizzy is still tight so there is no reasonfor it to be out surely but i know what your saying.
I think i'll change coil and plugs to eliminate them and take it from there and then thats all the ignition

This is the problem i am having mate!!

its very annoying i changed everything except coil but was getting sparks off all the plugs / leads so doubt its coil, i think mine is too much air!! it very annoying tho!!

if ya find the problem wud be kool if ya cud let me know and i will do the same for you!!