Vaccume .....Carburation.....Timing......maybee a bit of all three.
time to get the wrenches out and check carb bolts,,,,take a propane torch and while its running,,,turn the propane torch on,,unlitt,,,,,and send a little propane near your carb base plate,,and then your intake manifold to head join,,,,,if you notice a decent RPM difference,,then it may indicate,,,vaccume leak,,,near the point where the propane gets sucked in.
Dont do this for too long,,,,dont let propane build up,,let it disperse,,,,and go at it again.
Good luck