I can't spot anything, looks the common arrangement for hit and miss engines. Cam behind the timing gear moves the push rod, that moves the rocker and that moves the exhaust valve. Inlet is atmospheric and just opens when the vacuum cause by the descending piston sucks it open.

Before someone picks me up on it I should say it is not just hit and miss engines that can have this sort of inlet valve, many of the early engines did whatever means they were governed by or those that did not have a governor. does make it a bit easier to set them up, the spring is a lot weaker than that on the exhaust as it just needs enough strength to return the valve to the closed position

This is one of my engines being turned over by hand and you can see and hear the valve opening, the exhaust is on the side of the cylinder so you can't cee the pushrod operating that.

Most tend to hold the exhaust valve open rather than closed, that means the air is sucked in through the exhaust so no fuel/air mix enters via the inlet so the engine misses that ignition cycle.

You can see me manually doing what the governor does by holding the exhaust valve open on this test run as I had the governor disabled for initial tests. Inlet valve can also be seen working but not when exhaust held open.

Edited By JasonB on 07/11/2021 18:55:38