I had a similar problem with a Murray mower - turns out it was my
fault, not the unit. Because my grass was thick and wet, I had to
clean out the undercarriage a few times. When I did so, I tilted the
mower to reach underneath and pull out the clogged grass clippings
(after stopping the blade and turning the engine off, of course).

In doing so, I tipped the mower too much and flooded the carburetor,
resulting in a similar "lock up" that you seem to have.

A small engine shop in my neighborhood fixed me right up and warned me
about tipping the mower. "Always keep the carburetor on the high
side," he said.

With your previous carburetor problem, I wonder if that's where I would
question the dealer.

Good luck,
Squanklin