Some easy things to try before delving into more complex issues -
To see if it’s on one cylinder -
Start the engine and hold your hands over the exhaust outlets, they should feel the same or you could feel the colder blast of the miss-fire.
Swap over HT leads and see if the problem moves.
Check the pulley timing position Is correct on each cylinder.
If it’s on both, how old/good is your fuel?
