Engine Performance

How hard do most of you run your kars? Since mine is 44 years old, I tend to take it easy and baby my kar, however, when I do wind it out a bit, it seems to kind of run out energy at about 4500 to 5000 rpm. It is almost like the engine develops a skip or misses a bit. I don’t want to push it, so I’ve never run it at any higher rpm. I replaced the plugs and plug wires but it made no difference. Is there a simple “fix” or is that just the way it is?

My car has the stock Ford dual point distributor.

I've set the timing, but not replaced or gapped the points.