First let me echo what Keoke so aptly said, I may be old school when it comes to setting timing, but I never had an ear for tuning carbs by listening to the hiss from a hose...timing lights are a tried and true method too.
I respect others opinions but would offer that that the timing light is the best way to get the car to factory spec, but, I just read a timing question turn into a two page pus page discussion of how a timing light works or doesn't with our cars, and our cars are often not factory spec anymore, carbon build up in the head, raised compression ratio on a rebuild, lowered compression ratio from wear, wear to the distributor, timing mark wrong, different type of gas available now, are all reasons you may need to fine tune your timing for better performance or avoiding longevity killers.
The cars actually will run pretty well within a fairly broad range, with slight variations in temp and performance, but too much advance or too much retard is certainly bad. My main point to the OP is that I am guessing it is not a timing problem, which are seldom intermittent, and the car was probably closer to where it should have been when you started.
There are plenty of ways to do things, will add that for the professional the timing light to factory spec is going to be preferred because it is much quicker than the fine tuning by driving method.
I do use my light to test function of the advance weights and vacuum advance.
Andy:
Be live me Mate: " There is more than one way to skin a cat"----:highly_amused:
Which ever way you have perfected over the years works for you.