Hi Bob
Check that the top of the carb or body has not distorted,it does happen with Solex,but they do have a tendency to run rich,is it black smoking?
I assume you have checked/changed points,condenser,plugs,plug leads and HT lead and also distributor cap and carbon brush and spring. A possibility is that the springs on the auto advance in the bottom of the distibutor have weakened,this would cause the symptoms you are getting.
Let me know
Cheers
Degsy