Timing gear failure?

[paradocs#31]

What are the symptoms of a timing gear failure? My '31 A suddenly sputtered to a stop during a drive and stalled out and would not start or even fire with spark available at plugs. At the time I believed it was fouled fuel because there was some evidence of rust/flakes of sludge in gas drained from gas bowl through drain cock under Zenith 1 carb. After carb clean-up and new gaskets from Snyder's Antique Auto, what I observed was what appeared to be back pressure forcing gas to spray out of carb air vent on lower half of gas bowl when cranking engine over several times with elec starter. Any & all help would be greatly appreciated. Thx, JohnB