If you tumbling long enough you can usually smell the fuel coming out the exhaust.
Have you checked spark plugs.
That will also let you know if fuel is going to the cylinders.
I advise taking them out, clean/dry them if they are wet with fuel/oil.
Test to see if you are getting spark.
Reinsert 3 into the cylinders and connect their respective spark plug wires. leave one out and connect it and leave it resting on the engine (where it can't go anywhere but you can still see it); you can probably leave all 4 out but one is more manageable.
Do not have anyone holding the wire while you crank the engine over.(the electric shock can be severe; DO NOT HOLD WHILE CRANKING). If you see the spark more than likely the rest of the spark plugs are firing.
Hope you get through. Air is almost never a problem... It normally tends to be fuel or spark