Things that come to mind. All are cheap(no money, just time)
1, Put a dwell meter on it. Points that are gaped wrong will not work well. Dwell is fairly stable over a wide range of RPM(might help find a bad spring if the points float at higher RPM)
2, Pull the valve cover. Watch the rockers as you turn the motor over by hand. Reset the valve lash.
3, The "B" is not so bad(opinion). Is it leaking? Is it flooding?
4, Pull the plugs and see if they are wet,( oiled, or fuel). Check the gaps.
5, Undo the exhaust at the manifold. 2 nuts and some care. If the exhaust is plugged you will know.
6. Test the fuel pump. Pull the line at the carb, spin the motor and catch in a clean can.
6, The vacuum advance only works "on demand". At idle there is no vacuum signal to the advance on the dizzy. A movement of the butterfly will get a signal and the whole dizzy will move. Pull the vacuum line from the carb and test the advance unit. Be brave, you can make enough vacuum to move it(soap and water will help clean up the fitting before the "test".) Check the advance unit for leaking( Your tongue will work for this).
Advisory: Do one step at a time. Test and go to the next. It can help narrow down what is the issue and what is not.
The above posts are good ones, follow as best as you can. Let us know what you find and how it goes.
