85% of all thought to be carb problems are actually ignition problems.
Make sure the timing light mark is 8 to 12 degrees at idle with the vacuum advance hose disconnected. Raise the rpm while watching the timing mark and you will see the mechanical advance run up to about 22 degrees.
Now hook up the vacuum advance hose to the carb. You should use the ported connection. Ported will have no vacuum on it at idle. As you raise the rpm more vacuum will appear. The other connection is intake vacuum. This is less desirable connection. Either way you should get about 32 to 36 degrees of total timing at around 2500 rpm.
If this is all correct and you have no other vacuum leaks, you may have a carb problem. What carb are you running?