Q: Evaluating if the ignition timing is correct by ear on a car using leaded gas

Lead replacement actually does work. If it is an old enough car, you can advance the timing and then when you accelerate hard, especially if you are going uphill, if you hear the engine rattling a little when you accelerate, then see what the timing is and retard it a little.

Now, on a modern car you cannot do that because they got what is called MAP sensors. So, if you have timing too far advanced when you step on the gas, the computer would retard the timing automatically and you wouldn’t hear any rattle so you can’t do that. But, let’s face it--you can buy the timing light nowadays. You can go on eBay and buy it for like 15 bucks. So, you just buy timing light and hook it up. I have a video "how to set ignition timing in your car" and it is really simple to do.