Use the starter and "EOIC"
This means
Turn the engine until the EXHAUST just starts to OPEN and adjust that intake
Turn the engine until the INTAKE has fully opened and is nearly CLOSED and adjust that exhaust
This, by the way, works on anything with poppet valves from a Briggs single whanger to a V, a W, a Boxer, or an inline whatever
I can't speak for U engines
or big radials, but at my age I'm unlikely to need to know