Is this carbon buildup? And how can I fix this?
How can I fix this if that’s the issue?
Buy a timing light, a tachometer, and a golf tee.
Hook up the tachometer. If your car has a multi-spark CD ignition (such as MSD 6) then you'll need a tach that can work with the MSD tach output or some alternative to the old school types. If there is a tach in the car that works, its not ideal but will be good enough to get you started.
Find the timing marks. Clean.
Hook up the timing light. Run the wires so they won't get burned or cut.
Find the vacuum line running to the distributor. Remove it from the distributor and stick the golf tee in the hose.
Start the car and when the engine can be kicked down to slow idle, check the rpm and the timing.
