D 4 7 U rope start pony question

Timing slightly off or too much gas laying in the cylinders causing a hydro lock.

Thanks side-seat, I ALWAYS drain the heads before pulling the rope. Only a couple of drops of oil drain out, no fuel.

Does it feel like it's backfiring Angelo? Or does it feel like it just runs into a block and stops dead?

There is no backfire or miss at all. Purrs like a kitten when running. It just stops dead.  After it stops dead, I can easily rotate the flywheel by hand. It does not feel like anything is binding at all.

You might have a bad gear or tooth on your pony or magneto. I have seen some with a bit of debris that clung to a tooth and would cause that on occasion.
You need to upgrade to the Italian Stallion starter, powered by hops, but I have heard "it" is worn out now. JM

I believe there have been threads on the mag shaft braking on D4's on here. If I am remembering correctly the thrust bearing is letting the shaft walk back and forth. At some point the gear locks against the case. Mag shaft is the weak link that brakes. This might not be your problem, but it could be. So check the play in the crankshaft.