Hope he has bulletproof safety glasses...

I've owned a few 240Z over the years. 240Z's have twin SU carbs that need to be sync'd for the front 3 and rear 3 cylinders. Part of the carb sync process is to use a tool called a color tune; essentially a glass spark plug that lets you see the color of the flame. You adjust the air screw until the color goes from red to blue, and then dial it back until it's just yellow-ish blue.

Kind of the same process shown in that video.

I don't know a lot about engines running on natural gas - but I do know that the air/fuel ratio for natural gas has a very wide range.  Some of the vintage engines that run on natural gas can be set to run very/very slow.....the natural gas can burn very slowly and make a gentle push on the piston, and a smooth "whoosh" from the exhaust pipe.

https://www.youtube.com/watch?v=Bxr2hb0Hj9g

Early gas engines controlled speed/power in one of 3 ways.

Throttle Governed - These engines operated like a modern engine and the carb had a butterfly like a modern engine does.  The engine was set to run at a chosen speed, and when the governor sensed a change speed - it would open or close the throttle to keep the engine running at the set speed.

Hit & Miss - These engines did not have a butterfly in the carb (mixing valve) and the throttle was wide open all the time.  The speed of the engine was controlled by holding the exhaust valve open when the engine speed went over the set speed.  With the exhaust valve open a new charge of fuel/air would not be drawn into the engine, and there would not be a compression stroke.  When the engine speed dropped below the set speed the exhaust valve could close, and a new fuel/air charge would be pulled into the engine, and a power stroke would occur.  The engine in he video is not hooked up to anything - so it can go a long time between power pulses....when it was in operation and doing work it didn't miss nearly as many power strokes.

Volume Governed - A much rarer method of controlling engine speed was to control how long or how far the intake valve opened.  This would control the amount of fuel/air that could enter the engine with the intake valve....not with the carb.  

Here are a couple of the methods used to hold stop the engine from firing on a hit & miss engine.

Latch out:

https://www.youtube.com/watch?v=8iRYwRfsweA


Governor latch on exhaust push rod:
(Latch is the flat piece on the right side of the video)
https://www.youtube.com/watch?v=B8NVlKNQA1E