Questions for engine experts

[Mitch//pa]

when you put each cylinder on TDC and inject air you cannot let the piston move any as this will open a valve which is what happened in your case when air came out the carburetor.
i hold the crankshaft still at TDC using a wrench on the crank nut...

do a retest holding the crank still.
this wont cause oil burning but also remove the radiator cap when doing the leak down looking for air to come up..