All engines do not run best set to fire at 28 degrees BTDC. Just like all carb settings are not exactly 1 1/2 turns open.The 28 degrees is just a good place to start....also a guess of about 20 to 30 degress is a good enough starting point. Fine tune from there. The main thing that when your done it runs good. If the engine does not knock & idles good with a good top RPM...what more do you want???? I will go as far to say....I bet air races...ect have been lost by setting by a person that read 28 is the magic number and was beat out buy a guy that tunes by ear!!!! Capt,n