OS 4 Stroke Cam Timming ?
Since there is no ignition system, you got two shots at getting it right.
With the piston at Top Dead Center (TDC), the mark on the cam gear should be either straight down or straight up.
Once that's done, run it through a cycle and watch the valves:
1. TDC: Both valves closed
2. Down stroke #1: Both valves closed
3. Up stroke #1: Exhaust valve opens
4. TDC: Exhaust valve closes, intake valve opens
5. Down stroke #2: Intake valve opens
6. Up stroke #2: Both valves closed