There are lots of things that can cause that symptom. Advance is one of them for sure. Check the weights and springs under the points plate for gummed up residue and stuck weights. About an hour job to get in there and clean it all with some parts cleaner, and a wee brush or compressed air and then lube with some clean oil. I clean mine up when I change the points.
What year? Model or serial#
Check the fuel system after the dist. clean job.
The carb could be gunked up?
The accelerator pump not operating.
The accelerator pump might have leather in there.
It's possible it gotten old and brittle.
Or Ethanol has screwed it up.
Pics will help identify if you can't find any numbers.
So what does the distributor advance to? You can easily see it using and advance type timing light or timing tape. You can measure it while on muffs if you want.
You should be getting 21 degrees additional advance over your starting timing by the time you reach 3000 RPM
