Could I wip the inlet manifold off and rocker and move the engine via the crank so the inlets on cyln 4 car closed via the cam lobes then pour a tiny amount of petrol inside?
Hmmm....
If the valves are seating properly and the petrol stays put on the topside of the valves, you could soak it up with clean rag or blow it back out the intake plenum in the head with very low pressure air or even let it evaporate i suppose. That way you can prove the valves are ok without even taking the head off.
If it passes straight through the head and into the cylinder, then the heads gotta come off again anyway, and you can just wipe it dry with clean rag.
Worth a shot if you get toatally stumped with the logs/lambda theory.
However, Im a big believer that problems dont just appear (like the MAF theory), and thats it more likely to relate to either a fault not picked up at the time of the initial belt failure, or something has been omissed/disturbed during the rebuild itself.
Hope this comes to a conclusion soon!!
