I am assuming it is a magneto engine
Rather than using TDC as a reference look at the magnet in relation to the coil.
What works best for me is to start your flip with the magnet about 20 degrees before the coil.
Make it a fast, snappy flip.
You must have enough rotational speed for the coil to produce the spark when the magnet passes it.
Depending on the engine, the advance could be anywhere from 15 to 30 degrees BTC.
Also make sure the engine is well primed.

If it's electronic ignition I can't give you any info since all my engines are mag.