It would help if you understood engine operation...
The intake valve opens..piston goes down..sucks fuel into cylinder..
Intake valve closes...piston goes up..compresses fuel...sparkplug ignites fuel..piston goes down
Exhaust valve opens..piston goes up..burnt fuel forced out ...
Pull the valve covers...roll the engine over and make sure the valves are opening and closing..
If You Have All The Answers...Except The One You Need...You're Not Trying Hard Enough...
Do The Work