so it sounds to me like its starting but wont idle/run properly
1st thing is dont despair, with a little effort you will win.
check the idle solenoid before you go any further, could be the electrical connnection or the solenoid itself.
by the sounds of it you should pull the tank and flush it out, spray carby cleaner through the fuel lines then blow out with compressed air when the tank is off.
install new fuel filter and maybe consider pulling carby apart and clean out again.
Also check the timing and VERY important the points gap. this makes a huge difference as I found out.
![Cool 8)](./images/smilies/icon_cool.gif)