That is the main jet needle valve.
did u find out yet
Disassemble the carburetor and replace the needle and seat, following the manufacturers assembly and adjustment recommendations.
The plug gap for a 5.5 hp Tecumseh is .030 in.
Most often than not, an engine that stalls a few minutes after it starts is due to fuel starvation. Check the fuel filter and ensure it is clean. If the fuel filter is okay, open the carburetor needle valve about 1/8 turn for a slightly richer mixture.
The carburetor float may be stuck in the open position and allowing fuel to seep through the carburetor into the intake and into the cylinder. The needle may also not be seating correctly , check the float the check to make sure the needle is seated properly.
how many cc is a 13 hp
what is the capacity
From the Tecumseh Jiffy Drill website: Ratio for Tecumseh TVO85 (3 hp), AV520 (3 hp), AV600 (3.5 hp), TMO49 (2 hp), TC200 (1.6 hp) and TC300 (2 hp) engines is 40:1. For a 40:1 mixture: Mix 3.2 oz of 2-cycle oil to 1 gallon of gasoline.
Most likely the needle valve & seat in the carburetor bowl is defective allowing fuel to flow when the engine if off. This excess fuel will run into the cylinder and down to the crankcase. Replace the needle valve & seat.
Tecumseh website, "All spark plugs air gap is .030."
The fuel float may be stuck in the closed position. Or, the carburetor needle valve may be closed.
Tecumseh provides dealers with a 0.012" air gap guage, but 0.010 - 0.014" will do.