I'm gonna say that you might need a rebuild on that carb. But there are a few things that are cheaper to check first. If you want to check for a vacuum leak, get a propane torch bottle and with the engine running, crack it open unlit, and move the nozzle around any possible joints where a vacuum leak could have formed, like around the base of the carb, between the manifold and the heads, etc. If there is a vacuum leak, rpms will pick up when the propane gets sucked into the engine.
Another thing you can check for is a worn cap and rotor. Just pull the cap off and check for erosion. You'll usually see it on the blade of the rotor. Those are cheap to replace.
If everything checks out, then I think you might be getting close to carb rebuild time.
