what carb is this?

Mini Bike & Go-Kart Parts

I am sure its a member of the Pulsa jet line of carbs.
Its one of the later versions.

Provided it is the original carb on the engine you should be easily able to get a rebuild kit for it by providing the Briggs dealer with the modle and serial number stamped on cooling shroud.

I found some of the older Pulsa jets had two brass tubes inside the tanke that could come loose and drop out ( casuign the engine to starve for fuel ) or they themselves would become clogged with dirt ( and causing more fuel troubles ).

On the side of the carb is a small chamber that lifts fuel into the carb body from the tank.
This is a place where gum and varnish can build up and clog things that is sometimes missed.
Of the diaphram gets hard or stretched and does not allow proper fuel flow ( that is about the only thing that can go wrong on these ).

Take the carb off and check and clean these things.
The Pulsa jets were very reliable long used carbs.